代码随想录训练营第五十八章｜单调栈

今天是训练营第五十八天，是最后一天单调栈的开始

739. 每日温度 

class Solution {
    public int[] dailyTemperatures(int[] temperatures) {
        int n = temperatures.length;
        int[] res = new int[n];
        int[] stack = new int[n];
        int top = -1;
        for(int i = n-1; i>=0; i--){
            while(top >=0 &&temperatures[stack[top]]<=temperatures[i]){
                top--;
            }
            res[i] = top == -1 ? 0: stack[top] -i;
            stack[++top] = i;
        }
        return res;
    }
    
}

单调栈的模版题

496.下一个更大元素 I 

class Solution {
    public int[] nextGreaterElement(int[] nums1, int[] nums2) {
        Stack<Integer> temp = new Stack<>();
        int[] res = new int[nums1.length];
        Arrays.fill(res,-1);
        HashMap<Integer, Integer> hashMap = new HashMap<>();
        for (int i = 0 ; i< nums1.length ; i++){
            hashMap.put(nums1[i],i);
        }
        temp.add(0);
        for (int i = 1; i < nums2.length; i++) {
            if (nums2[i] <= nums2[temp.peek()]) {
                temp.add(i);
            } else {
                while (!temp.isEmpty() && nums2[temp.peek()] < nums2[i]) {
                    if (hashMap.containsKey(nums2[temp.peek()])){
                        Integer index = hashMap.get(nums2[temp.peek()]);
                        res[index] = nums2[i];
                    }
                    temp.pop();
                }
                temp.add(i);
            }
        }

        return res;
    }
}

题意比较难理解，要转化为单调栈问题

明天继续单调栈