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August 14, 2021 20:49
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4 Sum II
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| /* | |
| 454. 4Sum II | |
| Medium | |
| 2280 | |
| 85 | |
| Add to List | |
| Share | |
| Given four integer arrays nums1, nums2, nums3, and nums4 all of length n, return the number of tuples (i, j, k, l) such that: | |
| 0 <= i, j, k, l < n | |
| nums1[i] + nums2[j] + nums3[k] + nums4[l] == 0 | |
| Example 1: | |
| Input: nums1 = [1,2], nums2 = [-2,-1], nums3 = [-1,2], nums4 = [0,2] | |
| Output: 2 | |
| Explanation: | |
| The two tuples are: | |
| 1. (0, 0, 0, 1) -> nums1[0] + nums2[0] + nums3[0] + nums4[1] = 1 + (-2) + (-1) + 2 = 0 | |
| 2. (1, 1, 0, 0) -> nums1[1] + nums2[1] + nums3[0] + nums4[0] = 2 + (-1) + (-1) + 0 = 0 | |
| Example 2: | |
| Input: nums1 = [0], nums2 = [0], nums3 = [0], nums4 = [0] | |
| Output: 1 | |
| Constraints: | |
| n == nums1.length | |
| n == nums2.length | |
| n == nums3.length | |
| n == nums4.length | |
| 1 <= n <= 200 | |
| -228 <= nums1[i], nums2[i], nums3[i], nums4[i] <= 228 | |
| */ | |
| int fourSumCount(vector<int>& A, vector<int>& B, vector<int>& C, vector<int>& D) { | |
| unordered_map<int, int> abSum; | |
| for(auto a : A) { | |
| for(auto b : B) { | |
| ++abSum[a+b]; | |
| } | |
| } | |
| int count = 0; | |
| for(auto c : C) { | |
| for(auto d : D) { | |
| auto it = abSum.find(0 - c - d); | |
| if(it != abSum.end()) { | |
| count += it->second; | |
| } | |
| } | |
| } | |
| return count; | |
| } | |
| //https://leetcode.com/problems/4sum-ii/discuss/93925/Concise-C%2B%2B-11-code-beat-99.5 READ THE COMMENTS |
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