[pull] main from doocs:main

solution/0400-0499/0419.Battleships in a Board/README.md

@@ -25,7 +25,7 @@ tags:
 <p>&nbsp;</p>
 
 <p><strong>示例 1：</strong></p>
-<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0400-0499/0419.Battleships%20in%20a%20Board/images/battelship-grid.jpg" style="width: 333px; height: 333px;" />
+<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0400-0499/0419.Battleships%20in%20a%20Board/images/1719200420-KKnzye-image.png" style="width: 333px; height: 333px;" />
 <pre>
 <strong>输入：</strong>board = [["X",".",".","X"],[".",".",".","X"],[".",".",".","X"]]
 <strong>输出：</strong>2

solution/0500-0599/0503.Next Greater Element II/README.md

@@ -56,135 +56,15 @@ tags:
 
 <!-- solution:start -->
 
-### 方法一：单调栈 + 循环数组
+### 方法一：单调栈
 
-<!-- tabs:start -->
-
-#### Python3
-
-```python
-class Solution:
-    def nextGreaterElements(self, nums: List[int]) -> List[int]:
-        n = len(nums)
-        ans = [-1] * n
-        stk = []
-        for i in range(n << 1):
-            while stk and nums[stk[-1]] < nums[i % n]:
-                ans[stk.pop()] = nums[i % n]
-            stk.append(i % n)
-        return ans
-```
-
-#### Java
-
-```java
-class Solution {
-    public int[] nextGreaterElements(int[] nums) {
-        int n = nums.length;
-        int[] ans = new int[n];
-        Arrays.fill(ans, -1);
-        Deque<Integer> stk = new ArrayDeque<>();
-        for (int i = 0; i < (n << 1); ++i) {
-            while (!stk.isEmpty() && nums[stk.peek()] < nums[i % n]) {
-                ans[stk.pop()] = nums[i % n];
-            }
-            stk.push(i % n);
-        }
-        return ans;
-    }
-}
-```
-
-#### C++
-
-```cpp
-class Solution {
-public:
-    vector<int> nextGreaterElements(vector<int>& nums) {
-        int n = nums.size();
-        vector<int> ans(n, -1);
-        stack<int> stk;
-        for (int i = 0; i < (n << 1); ++i) {
-            while (!stk.empty() && nums[stk.top()] < nums[i % n]) {
-                ans[stk.top()] = nums[i % n];
-                stk.pop();
-            }
-            stk.push(i % n);
-        }
-        return ans;
-    }
-};
-```
-
-#### Go
-
-```go
-func nextGreaterElements(nums []int) []int {
-	n := len(nums)
-	ans := make([]int, n)
-	for i := range ans {
-		ans[i] = -1
-	}
-	var stk []int
-	for i := 0; i < (n << 1); i++ {
-		for len(stk) > 0 && nums[stk[len(stk)-1]] < nums[i%n] {
-			ans[stk[len(stk)-1]] = nums[i%n]
-			stk = stk[:len(stk)-1]
-		}
-		stk = append(stk, i%n)
-	}
-	return ans
-}
-```
-
-#### TypeScript
+题目需要我们找到每个元素的下一个更大元素，那么我们可以从后往前遍历数组，这样可以将问题为求上一个更大元素。另外，由于数组是循环的，我们可以将数组遍历两次。
 
-```ts
-function nextGreaterElements(nums: number[]): number[] {
-    const stack: number[] = [],
-        len = nums.length;
-    const res: number[] = new Array(len).fill(-1);
-    for (let i = 0; i < 2 * len - 1; i++) {
-        const j = i % len;
-        while (stack.length !== 0 && nums[stack[stack.length - 1]] < nums[j]) {
-            res[stack[stack.length - 1]] = nums[j];
-            stack.pop();
-        }
-        stack.push(j);
-    }
-    return res;
-}
-```
+具体地，我们从下标 $n \times 2 - 1$ 开始向前遍历数组，其中 $n$ 是数组的长度。然后，我们记 $j = i \bmod n$，其中 $\bmod$ 表示取模运算。如果栈不为空且栈顶元素小于等于 $nums[j]$，那么我们就不断地弹出栈顶元素，直到栈为空或者栈顶元素大于 $nums[j]$。此时，栈顶元素就是 $nums[j]$ 的上一个更大元素，我们将其赋给 $ans[j]$。最后，我们将 $nums[j]$ 入栈。继续遍历下一个元素。
 
-#### JavaScript
+遍历结束后，我们就可以得到数组 $ans$，它是数组 $nums$ 中每个元素的下一个更大元素。
 
-```js
-/**
- * @param {number[]} nums
- * @return {number[]}
- */
-var nextGreaterElements = function (nums) {
-    const n = nums.length;
-    let stk = [];
-    let ans = new Array(n).fill(-1);
-    for (let i = 0; i < n << 1; i++) {
-        const j = i % n;
-        while (stk.length && nums[stk[stk.length - 1]] < nums[j]) {
-            ans[stk.pop()] = nums[j];
-        }
-        stk.push(j);
-    }
-    return ans;
-};
-```
-
-<!-- tabs:end -->
-
-<!-- solution:end -->
-
-<!-- solution:start -->
-
-### 方法二
+时间复杂度 $O(n)$，空间复杂度 $O(n)$。其中 $n$ 是数组 $nums$ 的长度。
 
 <!-- tabs:start -->
 
@@ -241,8 +121,12 @@ public:
         stack<int> stk;
         for (int i = n * 2 - 1; ~i; --i) {
             int j = i % n;
-            while (!stk.empty() && stk.top() <= nums[j]) stk.pop();
-            if (!stk.empty()) ans[j] = stk.top();
+            while (stk.size() && stk.top() <= nums[j]) {
+                stk.pop();
+            }
+            if (stk.size()) {
+                ans[j] = stk.top();
+            }
             stk.push(nums[j]);
         }
         return ans;
@@ -259,7 +143,7 @@ func nextGreaterElements(nums []int) []int {
 	for i := range ans {
 		ans[i] = -1
 	}
-	var stk []int
+	stk := []int{}
 	for i := n*2 - 1; i >= 0; i-- {
 		j := i % n
 		for len(stk) > 0 && stk[len(stk)-1] <= nums[j] {
@@ -274,6 +158,27 @@ func nextGreaterElements(nums []int) []int {
 }
 ```
 
+#### TypeScript
+
+```ts
+function nextGreaterElements(nums: number[]): number[] {
+    const n = nums.length;
+    const stk: number[] = [];
+    const ans: number[] = Array(n).fill(-1);
+    for (let i = n * 2 - 1; ~i; --i) {
+        const j = i % n;
+        while (stk.length && stk.at(-1)! <= nums[j]) {
+            stk.pop();
+        }
+        if (stk.length) {
+            ans[j] = stk.at(-1)!;
+        }
+        stk.push(nums[j]);
+    }
+    return ans;
+}
+```
+
 #### JavaScript
 
 ```js
@@ -283,15 +188,15 @@ func nextGreaterElements(nums []int) []int {
  */
 var nextGreaterElements = function (nums) {
     const n = nums.length;
-    let stk = [];
-    let ans = new Array(n).fill(-1);
+    const stk = [];
+    const ans = Array(n).fill(-1);
     for (let i = n * 2 - 1; ~i; --i) {
         const j = i % n;
-        while (stk.length && stk[stk.length - 1] <= nums[j]) {
+        while (stk.length && stk.at(-1) <= nums[j]) {
             stk.pop();
         }
         if (stk.length) {
-            ans[j] = stk[stk.length - 1];
+            ans[j] = stk.at(-1);
         }
         stk.push(nums[j]);
     }