k sum(lintcode)

没通过的代码：

class Solution {
public:
    /*
     * @param A: An integer array
     * @param k: A positive integer (k <= length(A))
     * @param target: An integer
     * @return: An integer
     */
    int kSum(vector<int> &A, int k, int target) {
        // write your code here
        int length = A.size();
        vector<vector<vector< int> > > result(length+1,vector<vector<int > >(k+1,vetor<int >(target+1)));
        for(int i = 0;i <= length;i++)
            result[i][0][0] = 1;
        for(int i = 1;i <= length;i++){
            for(int j = 1;j <= k;j++){
                for(int p = 1;p <= target;p++){
                    if((p - A[i]) >= 0)
                        result[i][j][p] = result[i-1][j-1][p-A[i]] + result[i-1][j-1][p];
                    else
                        result[i][j][p] = result[i-1][j-1][p];
                }
            }
        }
        return result[length][k][target];
    }
};

 三维vector初始化：http://blog.csdn.net/u013630349/article/details/47777645