day45：单调栈篇

739.每日温度

class Solution {public int[] dailyTemperatures(int[] temperatures) {int n = temperatures.length;int[] ans = new int[n];Stack<Integer> stack = new Stack<>();stack.push(0);for (int i = 1; i < n; i++) {if (temperatures[i] <= temperatures[stack.peek()])stack.push(i);else {while (!stack.isEmpty() && temperatures[i] > temperatures[stack.peek()]) {ans[stack.peek()] = i - stack.pop();}stack.push(i);}}return ans;}
}

496.下一个更大元素 I

class Solution {public int[] nextGreaterElement(int[] nums1, int[] nums2) {Stack<Integer> stack = new Stack<>();int[] ans = new int[nums1.length];Arrays.fill(ans, -1);Map<Integer, Integer> map = new HashMap<>();for (int i = 0; i < nums1.length; i++)map.put(nums1[i], i);stack.push(0);for (int i = 1; i < nums2.length; i++) {if (nums2[i] <= nums2[stack.peek()])stack.push(i);else {while (!stack.isEmpty() && nums2[i] > nums2[stack.peek()]) {if (map.containsKey(nums2[stack.peek()])) {ans[map.get(nums2[stack.peek()])] = nums2[i];}stack.pop();}stack.push(i);}}return ans;}
}