题解 | #加起来和为目标值的组合(三)#

using System;
using System.Collections.Generic;


class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param k int整型
     * @param n int整型
     * @return int整型二维数组
     */
    public List<List<int>> combination (int k, int n) {
        // write code here
        List<List<int>> lslsN = new List<List<int>>();
        List<int> lsN = new List<int>();
        DG(k, n, ref lslsN, ref lsN, 0);
        return lslsN;
    }

    public static void DG(int k, int n, ref List<List<int>> lslsN,
                          ref List<int> lsN, int nCurIndex) {
        // write code here
        int nMaxLen = n - (1 + k) * k / 2;
        for (int nIndex = nCurIndex + 1; nIndex <= k + nMaxLen; nIndex++) {
            List<int> lsNCpy = new List<int>();
            lsNCpy.AddRange(lsN);
            lsNCpy.Add(nIndex);
            int nSum = 0;
            lsNCpy.ForEach(r => {
                nSum += r;
            });
            if (nSum > n)
                break;
            if (nSum == n && lsNCpy.Count == k) {
                lslsN.Add(lsNCpy);
                break;
            }
            DG(k, n, ref lslsN, ref lsNCpy, nIndex);
        }
    }
}