Leetcode#18 4Sum
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Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Note:
- Elements in a quadruplet (a,b,c,d) must be in non-descending order. (ie, a ≤ b ≤ c ≤ d)
- The solution set must not contain duplicate quadruplets.
For example, given array S = {1 0 -1 0 -2 2}, and target = 0. A solution set is: (-1, 0, 0, 1) (-2, -1, 1, 2) (-2, 0, 0, 2)
Difficulty: Medium
思路不是很难,可是Debug真是一件无比痛!苦!的事,足足花了我两个小时,可能还是不够熟练吧。
vector<vector<int> > fourSum(vector<int>& nums, int target) { vector<vector<int> > ans; int len = nums.size(); if(len<4) return ans; sort(nums.begin(),nums.end()); for(int p1 = 0; p1<len-3;p1++) { for(int p4 = p1+1; p4<len-2; p4++) { int p2 = p4+1, p3 = len-1; if(nums[p4]==nums[p4-1]&&p4-1>p1) continue; if(nums[p1]==nums[p1-1]&&p1>0) continue; while(p3>p2) { int target2 = target - nums[p1] - nums[p4]; if(nums[p2]==nums[p2-1]&&p2-1>p4) { p2++; continue; } if(nums[p3]==nums[p3+1]&&p3+1<len-1) { p3--; continue; } if(nums[p3]+nums[p2]>target2) { p3--; continue; } else if(nums[p3]+nums[p2]<target2) { p2++; continue; } else { vector<int> tmp; int test; tmp.push_back(nums[p1]); tmp.push_back(nums[p4]); tmp.push_back(nums[p2]); tmp.push_back(nums[p3]); ans.push_back(tmp); p2++; continue; } } }} return ans; }
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