Safecracker - 题目列表

题意

完整题面见同目录的 problem.md。

思路

代码

cpp

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73#include <bits/stdc++.h>
using namespace std;


int qua;
char letters[100];
int len;
char choose[10];
char ans[10];
int vis[100] = { 0 };
bool is_get_ans;

/* 求 a^n */
int _pow(int a,int n){
	int base = a;
	int ret =1;

	for(; n ; n = n >> 1){
		if(n & 1)//取最低位, 是不是很像判断奇偶
			ret = ret * base; //是1就乘
		base = base*base;     //base增增
	}

	return ret;
}
#define TO_INT(C) (C-'A'+1)
#define L(I) (TO_INT(choose[I]))

int calc(){
    return L(1)-_pow(L(2),2)+_pow(L(3),3)-_pow(L(4),4)+_pow(L(5),5);
}
void dfs(int dep){
    if( dep == 6){
        if( calc() == qua){
            is_get_ans = 1;
            memcpy(ans,choose,sizeof(ans));
        }

        return ;
    }
    int i;
    for(i=1;i<=len;i++){
        if( !vis[i]){
            choose[dep] = letters[i];
            vis[i] = 1;
            dfs(dep+1);
            vis[i] = 0;
        }
    }

}

int main(){
    while(1){

        scanf("%d",&qua);
        scanf("%s",letters+1);
        if( qua == 0)
            return 0;
        len = strlen(letters+1);
        sort(letters+1,letters+len+1);
        memset(vis,0,sizeof(vis));
        is_get_ans = 0;
        dfs(1);
        if( is_get_ans)
            printf("%s\n",ans+1);
        else
            printf("no solution\n");

    }

    return 0;
}

复杂度

总结

描述

“The item is locked in a Klein safe behind a painting in the second-floor library. Klein safes are extremely rare; most of them, along with Klein and his factory, were destroyed in World War II. Fortunately old Brumbaugh from research knew Klein’s secrets and wrote them down before he died. A Klein safe has two distinguishing features: a combination lock that uses letters instead of numbers, and an engraved quotation on the door. A Klein quotation always contains between five and twelve distinct uppercase letters, usually at the beginning of sentences, and mentions one or more numbers. Five of the uppercase letters form the combination that opens the safe. By combining the digits from all the numbers in the appropriate way you get a numeric target. (The details of constructing the target number are classified.) To find the combination you must select five letters v, w, x, y, and z that satisfy the following equation, where each letter is replaced by its ordinal position in the alphabet (A=1, B=2, …, Z=26). The combination is then vwxyz. If there is more than one solution then the combination is the one that is lexicographically greatest, i.e., the one that would appear last in a dictionary.” v - w2+ x3- y4+ z5= target “For example, given target 1 and letter set ABCDEFGHIJKL, one possible solution is FIECB, since 6 - 92+ 53- 34+ 25= 1. There are actually several solutions in this case, and the combination turns out to be LKEBA. Klein thought it was safe to encode the combination within the engraving, because it could take months of effort to try all the possibilities even if you knew the secret. But of course computers didn’t exist then.” "Develop a program to find Klein combinations in preparation for field deployment. Use standard test methodology as per departmental regulations.