Day58(739, 496)

739. Daily Temperatures

Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead.

Example 1:

Input: temperatures = [73,74,75,71,69,72,76,73]
Output: [1,1,4,2,1,1,0,0]

Example 2:

Input: temperatures = [30,40,50,60]
Output: [1,1,1,0]

Example 3:

Input: temperatures = [30,60,90]
Output: [1,1,0]

class Solution {  
    public int[] dailyTemperatures(int[] temperatures) {  
        int lens = temperatures.length;  
        int[] res = new int[lens];  
        Deque stack = new LinkedList<>();  
        for (int i = 0; i < lens; i++) {  
  
            while (!stack.isEmpty() && temperatures[i] > temperatures[stack.peek()]) {  
                res[stack.peek()] = i - stack.peek();  
                stack.pop();  
            }  
            stack.push(i);  
        }  
  
        return res;  
    }  
}

496. Next Greater Element I

The next greater element of some element x in an array is the first greater element that is to the right of x in the same array.

You are given two distinct 0-indexed integer arrays nums1 and nums2, where nums1 is a subset of nums2.

For each 0 <= i < nums1.length, find the index j such that nums1[i] == nums2[j] and determine the next greater element of nums2[j] in nums2. If there is no next greater element, then the answer for this query is -1.

Return an array ans of length nums1.length such that ans[i] is the next greater element as described above.

Example 1:

Input: nums1 = [4,1,2], nums2 = [1,3,4,2]
Output: [-1,3,-1]
Explanation: The next greater element for each value of nums1 is as follows:

• 4 is underlined in nums2 = [1,3,4,2]. There is no next greater element, so the answer is -1.
• 1 is underlined in nums2 = [1,3,4,2]. The next greater element is 3.
• 2 is underlined in nums2 = [1,3,4,2]. There is no next greater element, so the answer is -1.

Example 2:

Input: nums1 = [2,4], nums2 = [1,2,3,4]
Output: [3,-1]
Explanation: The next greater element for each value of nums1 is as follows:

• 2 is underlined in nums2 = [1,2,3,4]. The next greater element is 3.
• 4 is underlined in nums2 = [1,2,3,4]. There is no next greater element, so the answer is -1.

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