hdu 4192

dfs全排列  加  模拟计算

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#define maxn 10010
using namespace std;

bool vis[10];
int value[10], result, n, now[10],top;
char expr[100];
int check(int l, int r)
{
    if(l > r)
        return 0;
    int cnt = 0,p = -1,flag = 0;
    for(int i = l; i <= r; i++)
        if(expr[i] == '(')
            ++cnt;
        else if(expr[i] == ')')
            --cnt;
        else if((expr[i] == '+' || expr[i] == '-') && !cnt)
            flag = 1, p = i;
        else if((expr[i] == '*') && !cnt && !flag)
            p = i;
    if( p == -1 )
    {
        if( l == r )
        {
            return now[top++];
        }
        return check(l+1, r-1);
    }
    switch(expr[p])
    {
        case '+':
            return check(l,p-1) + check(p+1,r);
        case '-':
            return check(l,p-1) - check(p+1,r);
        case '*':
            return check(l,p-1) * check(p+1,r);
    }
    return 0;
}
int dfs(int cur)
{
    if( cur == n )
    {
        top = 0;
        int len = strlen(expr);
        if(check(0, len-1) == result)
            return 1;
//        printf("%d\n",check(0,len-1));
    }
    for(int i = 0; i < n; i++)
    {
        if( !vis[i] )
        {
            vis[i] = true;
            now[cur] = value[i];
            if(dfs(cur+1))
                return 1;
            vis[i] = false;
        }
    }
    return 0;
}
int main()
{
    while( scanf("%d",&n) == 1 )
    {
        if(n == 0)
        {
            scanf("%d",&result);
            if(result == 0)
                break;
        }
        for(int i = 0; i < n; i++) scanf("%d",&value[i]);
        scanf("%d",&result);
        scanf("%s",expr);
        int flag = 0;
        for(int i = 0; i < n; i++)
        {
            memset(vis, false, sizeof(vis));
            vis[i] = true;
            now[0] = value[i];
            if(dfs(1))
            {
                flag = 1;
                break;
            }
            vis[i] = false;
        }
        if( flag )   puts("YES");
        else          puts("NO");
    }
    return 0;
}

使用stl中的全排列函数

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#define maxn 10010
using namespace std;

int value[10], result, n, top;
char expr[100];
int check(int l, int r)
{
    if(l == r)
        return value[top++];
    int cnt = 0,p = -1,flag = 0;
    for(int i = l; i <= r; i++)
        if(expr[i] == '(')   cnt++;
        else if(expr[i] == ')')  cnt--;
        else if((expr[i] == '+' || expr[i] == '-') && !cnt)  flag = 1, p = i;
        else if((expr[i] == '*') && !cnt && !flag)  p = i;
    if( p == -1 )
        return check(l+1, r-1);
    switch(expr[p])
    {
    case '+':
        return check(l,p-1) + check(p+1,r);
    case '-':
        return check(l,p-1) - check(p+1,r);
    case '*':
        return check(l,p-1) * check(p+1,r);
    }
    return 0;
}

int main()
{
    while( scanf("%d",&n) == 1 )
    {
        if(n == 0)
        {
            scanf("%d",&result);
            if(result == 0)
                break;
        }
        for(int i = 0; i < n; i++) scanf("%d",&value[i]);
        scanf("%d",&result);
        scanf("%s",expr);
        int flag = 0;
        int len = strlen(expr);
        sort(value, value+n);
        do
        {
            top = 0;
            if(check(0, len-1) == result)
            {
                flag = 1;
                break;
            }
        }while(next_permutation(value, value+n));
        if( flag )   puts("YES");
        else         puts("NO");
    }
    return 0;
}