10400 game show math

第一次直接搜，20s的时限T了，没看题目说明。。。。。看了看别人的代码找到了一个很有效的剪枝。。。。1.835s过了。。。

legal函数是剪枝。

 

/**********************
* author:crazy_石头
* Pro:Problem H  Game Show Math
* algorithm:dfs
* Time:1.835s
* Judge Status:Accepted
***********************/
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <set>
#include <vector>

using namespace std;
#define rep(i,h,n) for(int i=(h);i<=(n);i++)
const int maxn=100+5;

bool ok;
int n,ret;
int a[maxn];
bool vis[maxn][32000<<1+5];
string ans;

inline bool legal(int x,int y)
{
    if (y>=-32000&&y<=32000&&!vis[x][y+32000])
    {
        vis[x][y+32000]=true;
        return true;
    }
    return false;
}

inline void dfs(int cur,int num,string s)//cur是搜到的层数，num存储当前计算结果，s为运算符
{
    if(ok)
        return;
    if(cur==n)
    {
        if(num==ret)
        {
            ok=1;
            rep(i,0,n-2)
            {
                printf("%d%c",a[i],s[i]);
            }
            printf("%d=%d\n",a[n-1],ret);
        }
        return ;
    }
    else
    {
        if(legal(cur+1,num+a[cur+1]))
            dfs(cur+1,num+a[cur+1],s+'+');
        if(legal(cur+1,num-a[cur+1]))
            dfs(cur+1,num-a[cur+1],s+'-');
        if(legal(cur+1,num*a[cur+1]))
            dfs(cur+1,num*a[cur+1],s+'*');
        if(a[cur+1]!=0&&num%a[cur+1]==0&&legal(cur+1,num/a[cur+1]))
            dfs(cur+1,num/a[cur+1],s+'/');
    }
}

int main()
{
    int test;
    scanf("%d",&test);
    while(test--)
    {
        memset(a,0,sizeof(a));
        memset(vis,0,sizeof(vis));
        scanf("%d",&n);
        rep(i,0,n-1)
            scanf("%d",&a[i]);
        scanf("%d",&ret);
        ok=0;
        dfs(0,a[0],ans);

        if(!ok)
            printf("NO EXPRESSION\n");
    }
    return 0;
}

* This source code was highlighted byYcdoiT. ( style: Desert )