Strange Printer — LeetCode 664 Python Solution

The problem

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.

Example

Input

s = "aaabbb"

Output

2

Explanation

Print "aaa" first and then print "bbb".

Python solution

class Solution:
    def strangePrinter(self, s: str) -> int:
        n = len(s)
        f = [[inf] * n for _ in range(n)]
        for i in range(n - 1, -1, -1):
            f[i][i] = 1
            for j in range(i + 1, n):
                if s[i] == s[j]:
                    f[i][j] = f[i][j - 1]
                else:
                    for k in range(i, j):
                        f[i][j] = min(f[i][j], f[i][k] + f[k + 1][j])
        return f[0][-1]

Complexity

Pattern: Dynamic Programming

Define a state, write the transition, and stop recomputing the same subproblem. LeetCode 664. Strange Printer is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Dynamic Programming.

The dynamic programming guide has the Python template for the pattern and the 481 LeetCode problems that use it.

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