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feat: add solutions to lc problem: No.1024
No.1024.Video Stitching
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‎solution/1000-1099/1024.Video Stitching/README.md

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<!-- 这里可写通用的实现逻辑 -->
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**方法一：贪心**
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注意到，如果相同起点的子区间有多个，那么选择右端点最大的那个子区间是最优的。
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因此，我们可以预处理所有子区间，对于每一个位置 $i$，算出所有以 $i$ 为起点的子区间中，右端点最大的那个位置，记录在数组 $last[i]$ 中。
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我们定义变量 `mx` 表示当前能够到达的最远位置，变量 `ans` 表示当前需要的最少子区间数，变量 `pre` 表示上一个被使用的子区间的右端点。
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接下来，我们从 $0$ 开始枚举所有位置 $i$，用 $last[i]$ 来更新 `mx`。如果更新后 $mx = i$，说明无法覆盖下一个位置，因此无法完成任务，返回 $-1$。
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同时我们记录上一个被使用的子区间的右端点 `pre`，如果 $pre = i$，说明需要使用一个新的子区间，因此我们将 `ans` 加 $1$，并将 `pre` 更新为 `mx`。
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遍历结束后，返回 `ans` 即可。
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时间复杂度 $O(n+m)$，空间复杂度 $O(m)$。其中 $n$ 和 $m$ 分别是数组 `clips` 的长度和 `time` 的值。
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
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class Solution:
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def videoStitching(self, clips: List[List[int]], time: int) -> int:
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last = [0] * time
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for a, b in clips:
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if a < time:
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last[a] = max(last[a], b)
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ans = mx = pre = 0
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for i, v in enumerate(last):
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mx = max(mx, v)
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if mx <= i:
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return -1
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if pre == i:
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ans += 1
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pre = mx
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return ans
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```
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### **Java**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```java
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class Solution {
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public int videoStitching(int[][] clips, int time) {
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int[] last = new int[time];
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for (var e : clips) {
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int a = e[0], b = e[1];
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if (a < time) {
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last[a] = Math.max(last[a], b);
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}
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}
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int ans = 0, mx = 0, pre = 0;
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for (int i = 0; i < time; ++i) {
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mx = Math.max(mx, last[i]);
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if (mx <= i) {
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return -1;
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}
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if (pre == i) {
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++ans;
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pre = mx;
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}
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}
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return ans;
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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int videoStitching(vector<vector<int>>& clips, int time) {
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vector<int> last(time);
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for (auto& v : clips) {
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int a = v[0], b = v[1];
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if (a < time) {
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last[a] = max(last[a], b);
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}
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}
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int mx = 0, ans = 0;
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int pre = 0;
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for (int i = 0; i < time; ++i) {
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mx = max(mx, last[i]);
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if (mx <= i) {
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return -1;
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}
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if (pre == i) {
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++ans;
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pre = mx;
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}
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}
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return ans;
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}
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};
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```
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### **Go**
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```go
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func videoStitching(clips [][]int, time int) int {
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last := make([]int, time)
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for _, v := range clips {
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a, b := v[0], v[1]
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if a < time {
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last[a] = max(last[a], b)
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}
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}
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ans, mx, pre := 0, 0, 0
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for i, v := range last {
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mx = max(mx, v)
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if mx <= i {
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return -1
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}
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if pre == i {
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ans++
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pre = mx
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}
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}
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return ans
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}
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func max(a, b int) int {
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if a > b {
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return a
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}
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return b
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}
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```
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### **...**

‎solution/1000-1099/1024.Video Stitching/README_EN.md

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Original file line numberDiff line numberDiff line change
@@ -60,13 +60,112 @@ Now we have segments [0,2] + [2,8] + [8,10] which cover the sporting event [0, 1
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### **Python3**
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```python
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class Solution:
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def videoStitching(self, clips: List[List[int]], time: int) -> int:
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last = [0] * time
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for a, b in clips:
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if a < time:
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last[a] = max(last[a], b)
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ans = mx = pre = 0
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for i, v in enumerate(last):
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mx = max(mx, v)
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if mx <= i:
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return -1
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if pre == i:
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ans += 1
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pre = mx
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return ans
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```
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### **Java**
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```java
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class Solution {
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public int videoStitching(int[][] clips, int time) {
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int[] last = new int[time];
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for (var e : clips) {
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int a = e[0], b = e[1];
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if (a < time) {
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last[a] = Math.max(last[a], b);
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}
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}
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int ans = 0, mx = 0, pre = 0;
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for (int i = 0; i < time; ++i) {
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mx = Math.max(mx, last[i]);
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if (mx <= i) {
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return -1;
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}
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if (pre == i) {
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++ans;
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pre = mx;
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}
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}
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return ans;
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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int videoStitching(vector<vector<int>>& clips, int time) {
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vector<int> last(time);
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for (auto& v : clips) {
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int a = v[0], b = v[1];
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if (a < time) {
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last[a] = max(last[a], b);
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}
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}
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int mx = 0, ans = 0;
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int pre = 0;
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for (int i = 0; i < time; ++i) {
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mx = max(mx, last[i]);
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if (mx <= i) {
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return -1;
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}
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if (pre == i) {
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++ans;
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pre = mx;
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}
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}
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return ans;
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}
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};
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```
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### **Go**
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```go
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func videoStitching(clips [][]int, time int) int {
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last := make([]int, time)
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for _, v := range clips {
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a, b := v[0], v[1]
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if a < time {
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last[a] = max(last[a], b)
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}
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}
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ans, mx, pre := 0, 0, 0
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for i, v := range last {
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mx = max(mx, v)
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if mx <= i {
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return -1
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}
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if pre == i {
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ans++
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pre = mx
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}
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}
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return ans
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}
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func max(a, b int) int {
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if a > b {
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return a
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}
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return b
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}
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```
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### **...**

‎solution/1000-1099/1024.Video Stitching/Solution.cpp

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Original file line numberDiff line numberDiff line change
@@ -1,24 +1,25 @@
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class Solution {
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public:
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int videoStitching(vector<vector<int>>& clips, int T) {
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int maxEnding = 0;
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int count = 0;
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vector<int> maxEnd(T + 1, 0); // maxEnd[i] : maximum ending time of all videos that start by time i
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for (int i = 0; i < clips.size(); ++i) {
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if (clips[i][0] >= T) continue;
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maxEnd[clips[i][0]] = max(maxEnd[clips[i][0]], clips[i][1]);
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}
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for (int i = 1; i < T; ++i) {
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maxEnd[i] = max(maxEnd[i], maxEnd[i - 1]);
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int videoStitching(vector<vector<int>>& clips, int time) {
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vector<int> last(time);
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for (auto& v : clips) {
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int a = v[0], b = v[1];
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if (a < time) {
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last[a] = max(last[a], b);
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}
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}
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for (int i = 0; i < T; ++i) {
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if (maxEnding == i) { // select video with maximum ending if one more video is necessary
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count++;
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maxEnding = maxEnd[i];
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} else if (maxEnding < i) {
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int mx = 0, ans = 0;
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int pre = 0;
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for (int i = 0; i < time; ++i) {
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mx = max(mx, last[i]);
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if (mx <= i) {
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return -1;
2017
}
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if (pre == i) {
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++ans;
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pre = mx;
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}
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}
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return count;
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return ans;
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}
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};

‎solution/1000-1099/1024.Video Stitching/Solution.go

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,28 @@
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func videoStitching(clips [][]int, time int) int {
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last := make([]int, time)
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for _, v := range clips {
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a, b := v[0], v[1]
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if a < time {
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last[a] = max(last[a], b)
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}
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}
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ans, mx, pre := 0, 0, 0
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for i, v := range last {
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mx = max(mx, v)
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if mx <= i {
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return -1
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}
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if pre == i {
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ans++
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pre = mx
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}
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}
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return ans
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}
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func max(a, b int) int {
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if a > b {
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return a
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}
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return b
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}

‎solution/1000-1099/1024.Video Stitching/Solution.java

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,23 @@
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class Solution {
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public int videoStitching(int[][] clips, int time) {
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int[] last = new int[time];
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for (var e : clips) {
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int a = e[0], b = e[1];
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if (a < time) {
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last[a] = Math.max(last[a], b);
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}
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}
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int ans = 0, mx = 0, pre = 0;
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for (int i = 0; i < time; ++i) {
12+
mx = Math.max(mx, last[i]);
13+
if (mx <= i) {
14+
return -1;
15+
}
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if (pre == i) {
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++ans;
18+
pre = mx;
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}
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}
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return ans;
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}
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}

‎solution/1000-1099/1024.Video Stitching/Solution.py

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,15 @@
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class Solution:
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def videoStitching(self, clips: List[List[int]], time: int) -> int:
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last = [0] * time
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for a, b in clips:
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if a < time:
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last[a] = max(last[a], b)
7+
ans = mx = pre = 0
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for i, v in enumerate(last):
9+
mx = max(mx, v)
10+
if mx <= i:
11+
return -1
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if pre == i:
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ans += 1
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pre = mx
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return ans

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