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feat: add solutions to lc/lcof2 problem: Random Pick With Weight
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‎lcof2/剑指 Offer II 071. 按权重生成随机数/README.md

+128-1
Original file line numberDiff line numberDiff line change
@@ -72,22 +72,149 @@ solution.pickIndex(); // 返回 0，返回下标 0，返回该下标概率为 1/
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<!-- 这里可写通用的实现逻辑 -->
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“前缀和 + 二分查找”。
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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 __init__(self, w: List[int]):
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n = len(w)
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self.presum = [0] * (n + 1)
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for i in range(n):
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self.presum[i + 1] = self.presum[i] + w[i]
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def pickIndex(self) -> int:
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n = len(self.presum)
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x = random.randint(1, self.presum[-1])
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left, right = 0, n - 2
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while left < right:
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mid = (left + right) >> 1
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if self.presum[mid + 1] >= x:
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right = mid
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else:
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left = mid + 1
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return left
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# Your Solution object will be instantiated and called as such:
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# obj = Solution(w)
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# param_1 = obj.pickIndex()
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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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private int[] presum;
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public Solution(int[] w) {
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int n = w.length;
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presum = new int[n + 1];
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for (int i = 0; i < n; ++i) {
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presum[i + 1] = presum[i] + w[i];
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}
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}
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public int pickIndex() {
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int n = presum.length;
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int x = (int) (Math.random() * presum[n - 1]) + 1;
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int left = 0, right = n - 2;
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while (left < right) {
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int mid = (left + right) >> 1;
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if (presum[mid + 1] >= x) {
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right = mid;
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} else {
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left = mid + 1;
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}
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}
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return left;
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}
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}
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/**
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* Your Solution object will be instantiated and called as such:
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* Solution obj = new Solution(w);
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* int param_1 = obj.pickIndex();
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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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vector<int> presum;
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Solution(vector<int>& w) {
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int n = w.size();
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presum.resize(n + 1);
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for (int i = 0; i < n; ++i) presum[i + 1] = presum[i] + w[i];
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}
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int pickIndex() {
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int n = presum.size();
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int x = rand() % presum[n - 1] + 1;
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int left = 0, right = n - 2;
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while (left < right)
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{
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int mid = left + right >> 1;
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if (presum[mid + 1] >= x) right = mid;
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else left = mid + 1;
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}
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return left;
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}
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};
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/**
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* Your Solution object will be instantiated and called as such:
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* Solution* obj = new Solution(w);
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* int param_1 = obj->pickIndex();
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*/
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```
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### **Go**
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```go
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type Solution struct {
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presum []int
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}
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func Constructor(w []int) Solution {
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n := len(w)
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pre := make([]int, n+1)
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for i := 0; i < n; i++ {
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pre[i+1] = pre[i] + w[i]
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}
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return Solution{pre}
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}
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func (this *Solution) PickIndex() int {
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n := len(this.presum)
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x := rand.Intn(this.presum[n-1]) + 1
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left, right := 0, n-2
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for left < right {
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mid := (left + right) >> 1
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if this.presum[mid+1] >= x {
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right = mid
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} else {
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left = mid + 1
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}
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}
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return left
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}
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/**
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* Your Solution object will be instantiated and called as such:
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* obj := Constructor(w);
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* param_1 := obj.PickIndex();
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*/
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```
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### **...**

‎lcof2/剑指 Offer II 071. 按权重生成随机数/Solution.cpp

+29
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,29 @@
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class Solution {
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public:
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vector<int> presum;
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Solution(vector<int>& w) {
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int n = w.size();
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presum.resize(n + 1);
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for (int i = 0; i < n; ++i) presum[i + 1] = presum[i] + w[i];
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}
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int pickIndex() {
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int n = presum.size();
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int x = rand() % presum[n - 1] + 1;
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int left = 0, right = n - 2;
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while (left < right)
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{
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int mid = left + right >> 1;
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if (presum[mid + 1] >= x) right = mid;
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else left = mid + 1;
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}
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return left;
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}
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};
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/**
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* Your Solution object will be instantiated and called as such:
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* Solution* obj = new Solution(w);
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* int param_1 = obj->pickIndex();
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*/

‎lcof2/剑指 Offer II 071. 按权重生成随机数/Solution.go

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,33 @@
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type Solution struct {
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presum []int
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}
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func Constructor(w []int) Solution {
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n := len(w)
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pre := make([]int, n+1)
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for i := 0; i < n; i++ {
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pre[i+1] = pre[i] + w[i]
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}
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return Solution{pre}
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}
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func (this *Solution) PickIndex() int {
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n := len(this.presum)
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x := rand.Intn(this.presum[n-1]) + 1
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left, right := 0, n-2
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for left < right {
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mid := (left + right) >> 1
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if this.presum[mid+1] >= x {
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right = mid
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} else {
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left = mid + 1
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}
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}
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return left
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}
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/**
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* Your Solution object will be instantiated and called as such:
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* obj := Constructor(w);
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* param_1 := obj.PickIndex();
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*/

‎lcof2/剑指 Offer II 071. 按权重生成随机数/Solution.java

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,32 @@
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class Solution {
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private int[] presum;
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public Solution(int[] w) {
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int n = w.length;
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presum = new int[n + 1];
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for (int i = 0; i < n; ++i) {
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presum[i + 1] = presum[i] + w[i];
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}
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}
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public int pickIndex() {
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int n = presum.length;
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int x = (int) (Math.random() * presum[n - 1]) + 1;
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int left = 0, right = n - 2;
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while (left < right) {
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int mid = (left + right) >> 1;
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if (presum[mid + 1] >= x) {
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right = mid;
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} else {
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left = mid + 1;
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}
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}
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return left;
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}
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}
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/**
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* Your Solution object will be instantiated and called as such:
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* Solution obj = new Solution(w);
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* int param_1 = obj.pickIndex();
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*/

‎lcof2/剑指 Offer II 071. 按权重生成随机数/Solution.py

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@@ -0,0 +1,23 @@
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class Solution:
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def __init__(self, w: List[int]):
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n = len(w)
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self.presum = [0] * (n + 1)
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for i in range(n):
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self.presum[i + 1] = self.presum[i] + w[i]
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def pickIndex(self) -> int:
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n = len(self.presum)
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x = random.randint(1, self.presum[-1])
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left, right = 0, n - 2
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while left < right:
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mid = (left + right) >> 1
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if self.presum[mid + 1] >= x:
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right = mid
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else:
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left = mid + 1
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return left
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# Your Solution object will be instantiated and called as such:
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# obj = Solution(w)
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# param_1 = obj.pickIndex()

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