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");
else
printf("Sorry,I can't!\n");
}

return 0;
}