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4Sum.cpp
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4Sum.cpp
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class Solution {
public:
vector<vector<int> > fourSum(vector<int> &num, int target) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
vector<vector<int> > result;
map<int, vector<vector<int> > > hash;
int len = num.size();
if (len < 4) return result;
vector<int> tmp(2);
for (int i = 0; i != len - 1; i++){
tmp[0] = i;
for (int j = i + 1; j != len; j++){
tmp[1] = j;
hash[num[i] + num[j]].push_back(tmp);
}
}
map<int, vector<vector<int> > >::iterator ite = hash.begin(), iend = hash.end();
for (; ite != iend; ite++){
vector<vector<int> > vec1 = ite->second, vec2 = hash[target-ite->first];
if (vec1.size() && vec2.size()){
for (int i = 0; i != vec1.size(); i++){
for (int j = 0; j != vec2.size(); j++){
if (vec1[i][0] != vec2[j][0] && vec1[i][1] != vec2[j][0] && vec1[i][0] != vec2[j][1] && vec1[i][1] != vec2[j][1]){
tmp.clear();
for (int k = 0; k != 2; k++){
tmp.push_back(num[vec1[i][k]]);
tmp.push_back(num[vec2[j][k]]);
}
sort(tmp.begin(), tmp.end());
result.push_back(tmp);
}
}
}
}
}
sort(result.begin(), result.end());
vector<vector<int> >::iterator uite = unique(result.begin(), result.end());
result.erase(uite, result.end());
return result;
}
};