Safecracker

问题陈述：

　　杭州电子科技大学HANGZHOU DIANZI UNIVERSITY Online Judge Problem - 1015

问题解析：

　　深度优先搜索(Depth_First Search)

代码详解：　　

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>

using namespace std;

int flag, visited[12];

int cmp(const void *a, const void *b){
    return *(char *)b - *(char *)a;
}

int calculate(char *ans) {
    int res = 0, x = 1, sign = 1;
    for(int i=0; i<5; i++) {
        for(int j=0; j<=i; j++) {
            x *= (ans[i] - 'A' + 1);
        }
        res += x * sign;
        x = 1;
        sign *= (-1);
    }
    return res;
}

void dfs(char *str, int target, char *ans, int depth, int len) {
    if(depth == 5) {
        if(calculate(ans) == target)
            flag = 1;
        return;
    }
    for(int i=0; i<len; i++) {
        if(!visited[i]) {
            ans[depth] = str[i];
            visited[i] = 1;
            dfs(str, target, ans, depth+1, len);
            if(flag)
                return;
            visited[i] = 0;
        }
    }
}

int main()
{
    int target;
    char ans[6], str[13];
    while(scanf("%d %s", &target, str)!=EOF && !(target==0 && strcmp(str, "END")==0)) {
        memset(visited, 0, sizeof(visited));
        qsort(str, strlen(str), sizeof(char), cmp);
        flag = 0;
        dfs(str, target, ans, 0, strlen(str));
        if(flag){
            ans[5] = '';
            puts(ans);
        } else {
            puts("no solution");
        }
    }
    return 0;
}

参考博客：CSDN Kizuki 

转载请注明出处：http://www.cnblogs.com/michaelwong/p/4315092.html