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3Sum.cpp
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51 lines (47 loc) · 1.51 KB
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/**
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.
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> &num) {
vector<vector<int> > ret;
if (num.empty()) return ret;
std::sort(num.begin(), num.end());
int n = num.size();
vector<int> triplet(3);
for (int i = 0; i < n; ++i) {
if (i >0&& num[i] == num[i-1]) continue;
int j = i+1;
int k = n-1;
while (j <k) {
int sum = num[i] + num[j] + num[k];
if (sum ==0) {
triplet[0] = num[i];
triplet[1] = num[j];
triplet[2] = num[k];
ret.push_back(triplet);
j ++;
k --;
//understand this two blocks
while (j <k && num[j] == num[j-1]) j++;
while (j <k &&num[k] == num[k+1]) k--;
}
else if(sum <0) {
j ++;
}
else {
k --;
}
}
}
return ret;
}
};