NYOJ 题目927 The partial sum problem（dfs,剪枝）

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The partial sum problem

时间限制：1000 ms | 内存限制：65535 KB

难度：2

描述

One day,Tom’s girlfriend give him an array A which contains N integers and asked him:Can you choose some integers from the N integers and the sum of them is equal to K.

输入

There are multiple test cases.
Each test case contains three lines.The first line is an integer N(1≤N≤20),represents the array contains N integers. The second line contains N integers,the ith integer represents A[i](-10^8≤A[i]≤10^8).The third line contains an integer K(-10^8≤K≤10^8).

输出

If Tom can choose some integers from the array and their them is K,printf ”Of course,I can!”; other printf ”Sorry,I can’t!”.

样例输入

41 2 4 71341 2 4 715

样例输出

Of course,I can!Sorry,I can't!

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ac代码

#include<string.h>#include<math.h>#include<stdio.h>#include<stdlib.h>int cmp(const void *a,const void *b){return *(int *)a-*(int *)b;}int a[30],n,sum,w,v[30];void dfs(int k,int cot){int i;if(cot==sum){w=1;return;}if(w)return;for(i=k;i<n;i++){if(i&&a[i]==a[i-1]&&!v[i-1])continue;if(cot>sum&&a[i]>0)return;v[i]=1;dfs(i+1,cot+a[i]);if(w)return;v[i]=0;}}int main(){while(scanf("%d",&n)!=EOF){int i;for(i=0;i<n;i++)scanf("%d",&a[i]);scanf("%d",&sum);qsort(a,n,sizeof(a[0]),cmp);w=0;memset(v,0,sizeof(v));dfs(0,0);if(w)printf("Of course,I can!\n");elseprintf("Sorry,I can't!\n");}}

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