题解 | #给表达式添加运算符#

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 num string字符串
     * @param target int整型
     * @return string字符串一维数组
     */
    public List<string> addOpt (string num, int target) {
        // write code here
        if (string.IsNullOrWhiteSpace(num) || (num.Length == 1 && num[0] != target))
            return null;
        List<string> lsStr = new List<string>();
        string strBDS = num.Substring(0, 1);
        DG(num, target, int.Parse(strBDS), 1, ref lsStr, strBDS);
        return lsStr;
    }

    public static void DG(string num, int target, int nCurR, int nL
                          , ref List<string> lsStr, string strBDS) {
        // write code here
        if (nCurR == target && nL == num.Length) {
            lsStr.Add(strBDS);
            return;
        }
        for (int nIndex = nL + 1; nIndex <= num.Length; nIndex++) {
            string strLeft = num.Substring(nL, nIndex - nL);
            int nLeft = int.Parse(strLeft);
            //'+'加法
            DG(num, target, nCurR + nLeft, nIndex, ref lsStr, strBDS + "+" + strLeft);
            //'-'减法
            DG(num, target, nCurR - nLeft, nIndex, ref lsStr, strBDS + "-" + strLeft);
            //'*'乘法
            DG(num, target, nCurR * nLeft, nIndex, ref lsStr, strBDS + "*" + strLeft);
            ////''拼接成多位数
            //int nAdd = strBDS.LastIndexOf('+');
            //int nSub = strBDS.LastIndexOf('-');
            //int nMul = strBDS.LastIndexOf('*');
            //int nMax = Math.Max(Math.Max(nAdd, nSub), nMul);
            //if (nMax < 0)
            //    nCurR = int.Parse(strBDS + strLeft);
            //else
            //{
            //    string strL
            //    switch (strBDS[nMax])
            //    {
            //        case '+':
            //            nCurR +=
            //            break;
            //        case '-':
            //            break;
            //        case '*':
            //            break;
            //    }
            //}
            //DG(num, target, nCurR - nLeft, nIndex, ref lsStr, strBDS + strLeft);
        }
    }
}