You are given two arrays (without duplicates) nums1
and nums2
where nums1
’s elements are subset of nums2
. Find all the next greater numbers for nums1
's elements in the corresponding places of nums2
.
The Next Greater Number of a number x in nums1
is the first greater number to its right in nums2
. If it does not exist, output -1 for this number.
Example 1:
Input: nums1 = [4,1,2], nums2 = [1,3,4,2]. Output: [-1,3,-1] Explanation: For number 4 in the first array, you cannot find the next greater number for it in the second array, so output -1. For number 1 in the first array, the next greater number for it in the second array is 3. For number 2 in the first array, there is no next greater number for it in the second array, so output -1.
Example 2:
Input: nums1 = [2,4], nums2 = [1,2,3,4]. Output: [3,-1] Explanation: For number 2 in the first array, the next greater number for it in the second array is 3. For number 4 in the first array, there is no next greater number for it in the second array, so output -1.
Note:
- All elements in
nums1
andnums2
are unique. - The length of both
nums1
andnums2
would not exceed 1000.
A:
哎,第二次,竟然没有想起来怎么做。
虽然也想到了用increasing stack, 可是还是不够理想
class Solution { public: vector<int> nextGreaterElement(vector<int>& nums1, vector<int>& nums2) { // keep an increaseing stack of nums2, from back to front stack<int> minStack; // top is the smallest int n1 = nums1.size(), n2 = nums2.size(); unordered_map<int, int> M; // value to its next grater for(int i = n2-1;i>=0;i--){ while(not minStack.empty() and minStack.top() <= nums2[i]){ minStack.pop(); } M[nums2[i]] = minStack.empty()?-1:minStack.top(); minStack.push(nums2[i]); } vector<int> res; for(int i =0;i<n1;i++) res.push_back(M[nums1[i]]); return res; } };
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