Leetcode: 15. 3Sum
2017-05-07 16:34
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Description
Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.Example
For example, given array S = [-1, 0, 1, 2, -1, -4], A solution set is: [ [-1, 0, 1], [-1, -1, 2] ]
思路
找出三个数的和0的所有情况。先排序
然后从前往后找 两个数的和是另外一个的负数。
注意区分重复情况。即一个数若已经找过了,那下一次出现重复时应该跳过。
这个题扎心了,一年前提交还是67ms,现在149ms,还是最好的一次情况。难道一年不见,大神们都成长这么快了吗
代码
class Solution { public: vector<vector<int>> threeSum(vector<int>& nums) { vector<vector<int>> res; int len = nums.size(); if(len <= 2) return res; int index1 = 0, index2 = 0; int i = 0 , s, e; sort(nums.begin(), nums.end()); for(i = 0; i < len; ++i){ if(i > 0 && nums[i] == nums[i - 1]) continue; s = i + 1; e = len - 1; while(s < e){ if(s > i + 1 && nums[s] == nums[s - 1]){ s++; continue; } if(e < len - 1 && nums[e] == nums[e + 1]){ e--; continue; } if(nums[s] + nums[e] > -nums[i]) e--; else if(nums[s] + nums[e] < -nums[i]) s++; else { vector<int> tmp; tmp.push_back(nums[i]); tmp.push_back(nums[s]); tmp.push_back(nums[e]); res.push_back(tmp); s++; } } } return res; } };
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