given an array of integers Find the index of values that satisfy A+B = C + D

martin_liang

于 2014-12-01 23:13:29 发布

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本文提供了一种算法解决给定数组中找到四个整数满足A+B=C+D的问题，并通过实例演示了解题过程。利用哈希表优化搜索效率，确保在复杂度上达到最优。

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转自：http://www.careercup.com/question?id=5652354158297088

You're given an array of integers(eg [3,4,7,1,2,9,8]) Find the index of values that satisfy A+B = C + D, where A,B,C & D are integers values in the array.

Eg: Given [3,4,7,1,2,9,8] array
The following
3+7 = 1+ 9 satisfies A+B=C+D
so print (0,2,3,5)

struct Node
{
    int x;
    int y;
    Node(int a=0, int b=0):x(a),y(b){};
};
vector<int> Print4Sum(vector<int> A){
    int tsum, l = A.size();
    vector<int> ans;
    if (l < 4) return ans;

    map<int, Node> hashmap;
    for (int i = 0; i < l-1; ++i)
        for (int j = i+1; j < l; ++j)
        {
            tsum = A[i] + A[j];
            if (hashmap.find(tsum) == hashmap.end()){
                Node tnode = Node(i,j);
                hashmap[tsum] = tnode;
            }else{
                Node tnode = hashmap[tsum];
                int x = tnode.x, y = tnode.y;
                if (x != i && x != j && y != i && y != j)
                {
                    ans.push_back(i);
                    ans.push_back(j);
                    ans.push_back(x);
                    ans.push_back(y);
                    sort(ans.begin(), ans.end());
                    return ans;
                }
            }
        }
    return ans;
}