Ultraviolet A 10344 23 out of 5 (search + full sorting)

Question: There are five counts and three arithmetic operations: +-*. can I obtain 23 for each arithmetic operation on five counts.

Train of Thought: simply search. Use next_permutation to find the sorting and search again.

//0 KB719 ms#include <stdio.h>#include <string.h>#include <algorithm>using namespace std;int a[5];bool flag;void DFS(int pre,int cur){    if (flag) return ;    if (cur == 5&&pre == 23)    {        flag = true;        return ;    }    if (cur > 4)        return ;    for (int i = 0;i < 3;i ++)    {        if (i == 0)            DFS(pre+a[cur],cur+1);        if (i == 1)            DFS(pre-a[cur],cur+1);        if (i == 2)            DFS(pre*a[cur],cur+1);    }}int main (){    #ifdef LOCAL        freopen("in.txt","r",stdin);    #endif    int i,cnt;    while (1)    {        cnt = 0;        for (i = 0;i < 5;i ++)        {            scanf ("%d",&a[i]);            if (!a[i])                cnt ++;        }        if (cnt == 5) break;        sort(a,a+5);        flag = false;        do        {            DFS(a[0],1);        }while (next_permutation(a,a+5)&&!flag);        if (flag) printf ("Possible\n");        else printf ("Impossible\n");    }    return 0;}