753. Cracking the Safe

753. Cracking the Safe

There is a box protected by a password. The password is n digits, where each letter can be one of the first k digits 0, 1, …, k-1.

You can keep inputting the password, the password will automatically be matched against the last n digits entered.

For example, assuming the password is “345”, I can open it when I type “012345”, but I enter a total of 6 digits.

Please return any string of minimum length that is guaranteed to open the box after the entire string is inputted.

Example 1:

Input: n = 1, k = 2Output: "01"Note: "10" will be accepted too.

Example 2:

Input: n = 2, k = 2Output: "00110"Note: "01100", "10011", "11001"

Note: n will be in the range [1, 4]. k will be in the range [1, 10]. k^n will be at most 4096.

class Solution { public String crackSafe(int n, int k) { int M = (int) Math.pow(k, n-1); int[] P = new int[M * k]; for (int i = 0; i < k; ++i) for (int q = 0; q < M; ++q) P[i*M + q] = q*k + i; StringBuilder ans = new StringBuilder(); for (int i = 0; i < M*k; ++i) { int j = i; while (P[j] >= 0) { ans.append(String.valueOf(j / M)); int v = P[j]; P[j] = -1; j = v; } } for (int i = 0; i < n-1; ++i) ans.append("0"); return new String(ans); }}

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