深度优先搜索的用法——求数组部分和

问题主题：求数组部分和

问题描述：

给定整数a1,a2, … an，判断能否从中选出若干个数，使得它们的和为k。

限制条件：

1<=n<=20

-10⁸<=a_i<=10⁸

-10⁸<=k<=10⁸

样例：

输入

n=4

a={1,2,4,7}

k=13

输出

Yes (13=2+4+7)

输入

n=4

a={1,2,4,7}

k=15

输出

    No

#include "stdafx.h"

#include "iostream"

using namespace std;

const int MAX = 10;

int     result;

int a[MAX];

int sum = 0;

bool resolve(int a[], int n, int i, int sum) ;

int _tmain(int argc, _TCHAR* argv[]) {

         int n;

         cout << "请?输º?入¨?n和¨ª结¨¢果?的Ì?大䨮小?:" <<endl;

         cin >> n >> result;

         cout << "请?输º?入¨?n个?数ºy:" <<endl;

         for(int i=0; i<n; i++) {

                   cin >> a[i];

         }

         if(resolve(a, n, 0, sum))

                   cout << "Yes" <<endl;

         else

                   cout << "No" << endl;

         return 0;

}

bool resolve(int a[], int n, int i, int sum) {

         if(i >= n)

                   return sum == result;

         //不?选?a[i]

         if(resolve(a, n, i+1, sum))

                   return true;

         //加¨®上¦?a[i]

         if(resolve(a, n, i+1, sum+a[i]))

                   return true;

         return false;

}

/**
 * User: luoweifu
 * Date: 14-1-7
 * Time: 上午11:33
 */
public class PartSum {
    private int array[];
    private int result;
    public PartSum() {
 
    }
 
    public PartSum(int[] array, int result) {
        this.array = array;
        this.result = result;
    }
 
       public void setArray(int[] array) {
              this.array = array;
       }
 
       public void setResult(int result) {
              this.result = result;
       }
 
       public boolean resolve(int[] array, int i, int sum) {
              int n = array.length;
              if(i >= n)
                     return sum == result;
              if(resolve(array, i+1, sum))
                     return true;
              if(resolve(array, i+1, sum+array[i]))
                     return true;
              return false;
       }
 
       public void partsumResolve() {
              if(resolve(array, 0, 0))
                     System.out.println("Yes");
              else
                     System.out.println("No");
       }
 
       public static void main(String args[]) {
              PartSum partSum = new PartSum(new int[]{1,2,4,7}, 13);
              partSum.partsumResolve();
              partSum.setResult(15);
              partSum.partsumResolve();
       }
 
}