# [LeetCode] 15. 3Sum 三数之和

Given an array S of n integers, are there elements abc in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

• Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)
• The solution set must not contain duplicate triplets.

    For example, given array S = {-1 0 1 2 -1 -4},

A solution set is:
(-1, 0, 1)
(-1, -1, 2)

class Solution {
public:
vector<vector<int>> threeSum(vector<int>& nums) {
vector<vector<int>> res;
sort(nums.begin(), nums.end());
if (nums.empty() || nums.back() < 0 || nums.front() > 0) return {};
for (int k = 0; k < (int)nums.size() - 2; ++k) {
if (nums[k] > 0) break;
if (k > 0 && nums[k] == nums[k - 1]) continue;
int target = 0 - nums[k], i = k + 1, j = (int)nums.size() - 1;
while (i < j) {
if (nums[i] + nums[j] == target) {
res.push_back({nums[k], nums[i], nums[j]});
while (i < j && nums[i] == nums[i + 1]) ++i;
while (i < j && nums[j] == nums[j - 1]) --j;
++i; --j;
} else if (nums[i] + nums[j] < target) ++i;
else --j;
}
}
return res;
}
};

class Solution {
public:
vector<vector<int>> threeSum(vector<int>& nums) {
set<vector<int>> res;
sort(nums.begin(), nums.end());
if (nums.empty() || nums.back() < 0 || nums.front() > 0) return {};
for (int k = 0; k < (int)nums.size() - 2; ++k) {
if (nums[k] > 0) break;
int target = 0 - nums[k], i = k + 1, j = (int)nums.size() - 1;
while (i < j) {
if (nums[i] + nums[j] == target) {
res.insert({nums[k], nums[i], nums[j]});
while (i < j && nums[i] == nums[i + 1]) ++i;
while (i < j && nums[j] == nums[j - 1]) --j;
++i; --j;
} else if (nums[i] + nums[j] < target) ++i;
else --j;
}
}
return vector<vector<int>>(res.begin(), res.end());
}
};

Github 同步地址：

https://github.com/grandyang/leetcode/issues/15

Two Sum

3Sum Smaller

3Sum Closest

4Sum

https://leetcode.com/problems/3sum/

https://leetcode.com/problems/3sum/discuss/7380/Concise-O(N2)-Java-solution

https://leetcode.com/problems/3sum/discuss/7373/Share-my-simple-java-solution

http://www.lifeincode.net/programming/leetcode-two-sum-3-sum-3-sum-closest-and-4-sum-java/

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posted @ 2015-05-06 13:01  Grandyang  阅读(89230)  评论(24编辑  收藏  举报