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To be honest, I dont like this problem. This is just an extra layer loop for 3sum. But two mistakes I had made…..
1. when skip j, use condition j > i+1. Because it starts from i+1. not from i.
2. Typo or my brain is gone… condition for l is num[l] == num[l+1] since l is decreasing.
1 class Solution { 2 public: 3 vector<vector<int> > fourSum(vector<int> &num, int target) { 4 vector<vector<int> > result; 5 int len = num.size(), i = 0, j = 0, k = 0, l = 0; 6 sort(num.begin(), num.end()); 7 for (i = 0; i < len-3; i++) { 8 if (i > 0 && num[i] == num[i-1]) continue; 9 for (j = i+1; j < len-2; j++) { 10 if (j > i+1 && num[j] == num[j-1]) continue; 11 k = j+1, l = len-1; 12 while (k < l) { 13 int sum = num[i] + num[j] + num[k] + num[l]; 14 if (sum > target) l--; 15 else if (sum < target) k++; 16 else { 17 vector<int> tmp; 18 tmp.push_back(num[i]); 19 tmp.push_back(num[j]); 20 tmp.push_back(num[k]); 21 tmp.push_back(num[l]); 22 result.push_back(tmp); 23 do{k++;} while (k < l && num[k] == num[k-1]); 24 do{l--;} while (k < l && num[l] == num[l+1]); 25 } 26 } 27 } 28 } 29 return result; 30 } 31 };
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原文地址：http://www.cnblogs.com/shuashuashua/p/4346152.html
