Safecracker（HDU1015 全排列回溯）

題目鏈接

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <string>
#include <cmath>
#include <queue>
using namespace std;
int num, len;
char letter[15];
int flag;
int vis[15];
bool cmp(char a, char b)
{
    return a > b;
}
int p(int n, int i)
{
    int j, sum = 1;
    for(j = 0; j < i; j++)
        sum *= n;
    return sum;
}
void dfs(int j, char tmp[])
{
    if(j == 5)
    {
       if((tmp[0]-'A'+1) - p(tmp[1]-'A'+1, 2) + p(tmp[2]-'A'+1, 3) - p(tmp[3]-'A'+1, 4) + p(tmp[4]-'A'+1, 5) == num)
        {
            flag = 1;
            tmp[5] = '\0';
            cout << tmp << endl;
        }
    }
    else
    {
        if(flag == 1)
            return;
        int i;
        for(i = 0; i < len; i++)
        {
            if(!vis[i])
            {
                vis[i] = 1;
                tmp[j] = letter[i];
                dfs(j+1, tmp);
                vis[i] = 0;
            }
        }
    }
}
int main()
{
    while(cin >> num >> letter)
    {
        if(num == 0 && strcmp(letter, "END") == 0)
            break;
        len = strlen(letter);
        sort(letter, letter+len, cmp);
        flag = 0;
        memset(vis, 0, sizeof(vis));
        char tmp[13];
        dfs(0, tmp);
        if(flag == 0)
            cout << "no solution" << endl;
    }
    return 0;
}