Sicily-1050 深度优先搜索

一．      题意

给出5个数和4则运算，看能不能算出目标值出来，如果算不出来就算出比目标值小的最大值。深搜：每一步选两个数做运算，然后算出的结果作为下一步的其中一个操作数。每一步选数有C(5,2)种，每两个数间又有5种运算结果（减法位置不同算两种）。

二．      做法：

用数组存储放进来的5各操作数，并在这个过程中用来存放中间答案，没进行一次计算操作数的个数就会减少一个。注意每一步深搜之后都要恢复原本状态。

三．      源码

 //
 //  main.cpp
 //  sicily-1050
 //
 //  Created by ashley on 14-10-10.
 //  Copyright (c) 2014年 ashley. All rights reserved.
 //

 #include <iostream>
 using namespace std;
 int storing[];
 int answer, result;
 void depthSearch(int size)
 {
     for (int i = ; i < size; i++) {
         if (storing[i] > result && storing[i] <= answer) {
             result = storing[i];
         }
     }
     if (result == answer) {
         return;
     }
     if (size == ) {
         return;
     }
     for (int i = ; i < size - ; i++) {
         for (int j = i + ; j < size; j++) {
             int left, right;
             left = storing[i];
             right = storing[j];
             storing[j] = storing[size - ];
             //add and decrease a number
             storing[i] = left + right;
             depthSearch(size - );
             //subtract and decrease a number
             storing[i] = left - right;
             depthSearch(size - );
             //subtract and decrease a number
             storing[i] = right - left;
             depthSearch(size - );
             //multiply and decrease a number
             storing[i] = left * right;
             depthSearch(size - );
             //divide and decrease a number
             if (left !=  && right % left == ) {
                 storing[i] = right / left;
                 depthSearch(size - );
             }
             if (right !=  && left % right == ) {
                 storing[i] = left / right;
                 depthSearch(size - );
             }
             storing[i] = left;
             storing[j] = right;
         }
     }
 }
 int main(int argc, const char * argv[])
 {
     int runs;
     cin >> runs;
     while (runs--) {
         for (int i = ; i < ; i++) {
             cin >> storing[i];
         }
         cin >> answer;
         result = -;
         depthSearch();
         cout << result << endl;
     }
     return ;
 }