链接: 739. 每日温度
链接: 496.下一个更大元素 I

739. 每日温度

单调栈入门题

这题的关键时保证了栈内所有的元素都是单调递增的（单调栈）

class Solution {public int[] dailyTemperatures(int[] temperatures) {Deque<Integer> stack = new LinkedList<>();int[] res = new int[temperatures.length];stack.push(0);for(int i = 1; i < temperatures.length; i++){if(temperatures[i] <= temperatures[stack.peek()]){ // 当遍历的温度小于等于栈顶元素时则加入栈中stack.push(i);}else{while(!stack.isEmpty() && temperatures[i] > temperatures[stack.peek()]){ // 当遍历的温度大于栈顶元素且栈不为空时则记录结果并将结果弹出res[stack.peek()] = i - stack.peek();stack.pop();}stack.push(i); // 当栈顶元素大于遍历的温度时则加入栈}}return res;}
}

496.下一个更大元素 I

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