poj 2362 Square

#include<iostream>#include<stdio.h>#include<algorithm>using namespace std;int a[100],b[100],n,sum;bool d;void dog(int x,int y,int z){    int i;    if (x==0) {d=true;return;}    if (z==0)    {        for(i=1;i<=n;i++)          if (b[i]==0)    {     b[i]=1;     dog(x-1,i+1,sum/4-a[i]);     b[i]=0;     return ;    }    } if (y>n) return ;    for(i=y;i<=n;i++)    if (b[i]==0)    {  if (b[i-1]==0&&a[i]==a[i-1]) continue;        if(z>=a[i])        {  b[i]=1; dog(x-1,i+1,z-a[i]); b[i]=0; if (d) return ;        }      }}bool cmp(int x,int y){    if (x>y) return true;    return false;}int main(){    int t,ii,i,max;    scanf("%d",&t);    for(ii=1;ii<=t;ii++)    {        scanf("%d",&n);        sum=0;        max=0;        for(i=1;i<=n;i++)        { scanf("%d",&a[i]); sum+=a[i]; if (a[i]>max) max=a[i];        }        if (sum%4!=0) {printf("non");continue;}        if (max>sum/4){printf("non");continue;}        sort(a+1,a+n+1,cmp);        d=false;        for(i=1;i<=n;i++)          b[i]=0;  b[0]=1;  a[0]=-100000;        b[1]=1;        dog(n-1,2,sum/4-a[1]);        if (d) printf("yesn");        elseprintf("non");    }    return 0;}