3 Sum O(n^2) about acm-icpc-algorithms HOT 6 CLOSED

for (int i=0; i<n-1; i++) 
{ 
    unordered_set<int> s; 
    for (int j=i+1; j<n; j++) 
    { 
        int x = -(arr[i] + arr[j]); 
        if (s.find(x) != s.end()) 
        { 
            printf("%d %d %d\n", x, arr[i], arr[j]); 
            found = true; 
        } 
        else
            s.insert(arr[j]); 
    } 
} 

if (found == false) 
    cout << " No Triplet Found" << endl;