10344UVA算23点

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这个方法0.33（一遍全排列一遍求“23”）比上次那个0.15（用next_permutation生成全排序，在递归求“23”）慢一点

#include<stdio.h>#include<string.h>int arr[5];bool used[5];bool sum23(int cur,int sum){if(cur == 5){if(sum == 23)return true;else return false;}bool res = false;for(int i = 0; i < 5; ++i){if(!used[i]){used[i] = true;res = res || sum23(cur+1,sum+arr[i]);res = res || sum23(cur+1,sum-arr[i]);res = res || sum23(cur+1,sum*arr[i]);if(res)return true;used[i] = false;}}return res;}int main(){freopen("input.txt","r",stdin);freopen("out.txt","w",stdout);while(scanf("%d%d%d%d%d",arr,arr+1,arr+2,arr+3,arr+4)==5){if(!arr[0]&&!arr[1]&&!arr[2]&&!arr[3]&&!arr[4])break;bool ok = false;memset(used,false,sizeof(used));for(int i=0; i < 5; ++i){used[i] = true;if(sum23(1, arr[i])){ok = true;break;}used[i] = false;}if(ok){printf("Possible\n");}else{printf("Impossible\n");}}}

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