Codeforces Round #394 (Div. 2) C. Dasha and Password 贪心+预处理+枚举
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After overcoming the stairs Dasha came to classes. She needed to write a password to begin her classes. The password is a string of length n which satisfies the following requirements:
- There is at least one digit in the string,
- There is at least one lowercase (small) letter of the Latin alphabet in the string,
- There is at least one of three listed symbols in the string: '#', '*', '&'.
Considering that these are programming classes it is not easy to write the password.
For each character of the password we have a fixed string of length m, on each of these n strings there is a pointer on some character. The i-th character displayed on the screen is the pointed character in the i-th string. Initially, all pointers are on characters with indexes1 in the corresponding strings (all positions are numbered starting from one).
During one operation Dasha can move a pointer in one string one character to the left or to the right. Strings are cyclic, it means that when we move the pointer which is on the character with index 1 to the left, it moves to the character with the index m, and when we move it to the right from the position m it moves to the position 1.
You need to determine the minimum number of operations necessary to make the string displayed on the screen a valid password.
The first line contains two integers n, m (3 ≤ n ≤ 50, 1 ≤ m ≤ 50) — the length of the password and the length of strings which are assigned to password symbols.
Each of the next n lines contains the string which is assigned to the i-th symbol of the password string. Its length is m, it consists of digits, lowercase English letters, and characters '#', '*' or '&'.
You have such input data that you can always get a valid password.
Print one integer — the minimum number of operations which is necessary to make the string, which is displayed on the screen, a valid password.
3 41**2a3*0c4**
1
5 5#*&#**a1c&&q2w*#a3c#*&#*&
3
In the first test it is necessary to move the pointer of the third string to one left to get the optimal answer.
In the second test one of possible algorithms will be:
- to move the pointer of the second symbol once to the right.
- to move the pointer of the third symbol twice to the right.
Source
Codeforces Round #394 (Div. 2)
My Solution
题意:长度为n的密码必须包含至少一个字母一个数字一个非字母非数字的字符,给出n个长度为m的字符串,每个串取一个字符,要求移动最少的步数使所成的密码为合法的密码。
贪心+预处理+枚举
先贪心的预处理出每个字符串 v[i]的v[i].c表示移动到字母的最少步数,v[i].d表示移动到数字的最少步数,v[i].f表示移动到其它字符的最少步数。
先把.c.d.f都初始化为INF,然后扫一遍字符串,如果不存在相应的请求则值依然是INF。
因为n <= 50 所以显然是n^3的枚举,即枚举每一个.c.d.f要求它们来自不同的3个ijk。这样就不会漏掉什么情况了 Y ^_^ Y。
复杂度 O(n^3)
#include <iostream>#include <cstdio>#include <string>#include <cstring>using namespace std;typedef long long LL;const int maxn = 1e2 + 8;const int INF = 1e9 + 8;string s[maxn];struct p{ int d, c, f;}v[maxn];int main(){ #ifdef LOCAL freopen("c.txt", "r", stdin); //freopen("c.out", "w", stdout); int T = 4; while(T--){ #endif // LOCAL ios::sync_with_stdio(false); cin.tie(0); int n, m, i, j, k, cnt; cin >> n >> m; for(i = 0; i < n; i++){ cin >> s[i]; } //memset(v, -1, sizeof v); for(i = 0; i < n; i++){ v[i].c = v[i].d = v[i].f = INF; cnt = 0; for(j = 0; j < m; j++){ if(isalpha(s[i][j])) v[i].c = min(v[i].c ,cnt); else if(isdigit(s[i][j])) v[i].d = min(v[i].d, cnt); else v[i].f = min(cnt, v[i].f); cnt++; } cnt = 1; for(j = m - 1; j >= 0; j--){ if(isalpha(s[i][j])) v[i].c = min(v[i].c ,cnt); else if(isdigit(s[i][j])) v[i].d = min(v[i].d, cnt); else v[i].f = min(cnt, v[i].f); cnt++; } } int ans = INF; for(i = 0; i < n; i++){ if(v[i].c == INF) continue; for(j = 0; j < n; j++){ if(v[j].d == INF || i == j) continue; for(k = 0; k < n; k++){ if(v[k].f == INF || i == k || j == k) continue; ans = min(ans, v[i].c + v[j].d + v[k].f); } } } cout << ans << endl; #ifdef LOCAL cout << endl; } #endif // LOCAL return 0;}
Thank you!
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