NYOJ927The partial sum problem

The partial sum problem

时间限制：1000 ms  |  内存限制：65535 KB

难度：3

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!”.

#include "stdio.h"#include "stdlib.h"#include "string.h"int N, P, a[25];int Mcmp(const void *_a, const void *_b){int * a =  (int *)_a;int *b = (int *)_b;return *a-*b;}int dfs(int s, int sum){if(sum == P)return 1;if(s == N ||(P>0&&a[s] > P)||(sum>0&&sum > P))return 0; if(dfs(s+1, sum+a[s]))     return 1;else     return dfs(s+1, sum);}int main(int argc, char *argv[]) {int i;while(scanf("%d", &N) != EOF){for(i = 0; i < N; i++)scanf("%d", &a[i]);scanf("%d", &P);qsort(a, N, sizeof(int), Mcmp);if(dfs(0, 0))printf("Of course,I can!\n");elseprintf("Sorry,I can't!\n");}return 0;}