LeetCode-3Sum -三数求和-有序数组扫描

typedef pair<int,pair<int,int>> scpair;
class Solution {
public:
    int m,n;
    vector<vector<int> > threeSum(vector<int> &num) {
        n=num.size();
        vector<vector<int> > res;
        if (n<3) return res;
        vector<int> &a=num;
        set   <scpair> st;
        sort(a.begin(),a.end());
        for (int i=0;i<n-2;i++) {
            scpair cr;
            cr.first=a[i];
            int l=i+1;
            int r=n-1;
            int x=0-a[i];
            while(l<r){
                int cs=a[l]+a[r];
                if (cs<x) l++;
                else if(cs>x) r--;
                else {
                    cr.second.first =a[l];
                    cr.second.second=a[r];
                    st.insert(cr);
                    l++;
                }
            }
        }
        for (auto it=st.begin();it!=st.end();it++) {
            vector<int> cur(3,0);
            cur[0]=it->first;
            cur[1]=it->second.first;
            cur[2]=it->second.second;
            res.push_back(cur);
        }
        return res;
    }
};