LeetCode-in-Java

664. Strange Printer

Hard

There is a strange printer with the following two special properties:

• The printer can only print a sequence of the same character each time.
• At each turn, the printer can print new characters starting from and ending at any place and will cover the original existing characters.

Given a string s, return the minimum number of turns the printer needed to print it.

Example 1:

Input: s = “aaabbb”

Output: 2

Explanation: Print “aaa” first and then print “bbb”.

Example 2:

Input: s = “aba”

Output: 2

Explanation: Print “aaa” first and then print “b” from the second place of the string, which will cover the existing character ‘a’.

Constraints:

• 1 <= s.length <= 100
• s consists of lowercase English letters.

Solution

public class Solution {
    public int strangePrinter(String s) {
        if (s.isEmpty()) {
            return 0;
        }
        int[][] dp = new int[s.length()][s.length()];
        for (int i = s.length() - 1; i >= 0; i--) {
            for (int j = i; j < s.length(); j++) {
                if (i == j) {
                    dp[i][j] = 1;
                } else if (s.charAt(i) == s.charAt(i + 1)) {
                    dp[i][j] = dp[i + 1][j];
                } else {
                    dp[i][j] = dp[i + 1][j] + 1;
                    for (int k = i + 1; k <= j; k++) {
                        if (s.charAt(k) == s.charAt(i)) {
                            dp[i][j] = Math.min(dp[i][j], dp[i + 1][k - 1] + dp[k][j]);
                        }
                    }
                }
            }
        }
        return dp[0][s.length() - 1];
    }
}

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