POJ 1564(HDU 1258 ZOJ 1711) Sum It Up（DFS）

题目链接：http://poj.org/problem?id=1564

题目大意：给定一个整数t，和n个元素组成的集合。求能否用该集合中的元素和表示该整数，如果可以输出所有可行解。1<=n<=12

Sample Input

4 6 4 3 2 2 1 1
5 3 2 1 1
400 12 50 50 50 50 50 50 25 25 25 25 25 25
0 0

Sample Output

Sums of 4:
4
3+1
2+2
2+1+1
Sums of 5:
NONE
Sums of 400:
50+50+50+50+50+50+25+25+25+25
50+50+50+50+50+25+25+25+25+25+25

分析：

代码如下：

 # include<cstdio>
 # include<iostream>
 # include<algorithm>
 using namespace std;
 bool cmp(int a,int b){
     return a>b;
 }
 int a[],t,n;
 bool flag;
 int ans[],len;

 void dfs(int sum,int mark){
     int i;
     if(sum == ){
         flag = true;
         printf("%d",ans[]);
         for(i=;i<len;i++)
             printf("+%d",ans[i]);
         printf("\n");
         return;
     }
     if(sum< || mark>=n) return ;
     for(i=mark; i<n; i++){
         if(i==mark || a[i] != a[i-]){
             ans[len++] = a[i];
             dfs(sum-a[i],i+);
             len--;
         }
     }
 }
 int main(){
     int i;
     while(scanf("%d%d",&t,&n) && n){
         int temp = ;
         for(i=;i<n;i++){
             scanf("%d",&a[i]);
             temp += a[i];
         }
         printf("Sums of %d:\n",t);
         if(temp<t){
             printf("NONE\n");
             continue;
         }
         flag = false;
         len = ;
         sort(a,a+n,cmp);
         dfs(t,);
         if(!flag)
             printf("NONE\n");

     }
     return ;
 }