Substring With Largest Variance — LeetCode 2272 Python Solution

The problem

The variance of a string is defined as the largest difference between the number of occurrences of any 2 characters present in the string. Note the two characters may or may not be the same.

Example

Input

s = "aababbb"

Output

3

Explanation

All possible variances along with their respective substrings are listed below:

Python solution

class Solution:
    def largestVariance(self, s: str) -> int:
        ans = 0
        for a, b in permutations(ascii_lowercase, 2):
            if a == b:
                continue
            f = [0, -inf]
            for c in s:
                if c == a:
                    f[0], f[1] = f[0] + 1, f[1] + 1
                elif c == b:
                    f[1] = max(f[1] - 1, f[0] - 1)
                    f[0] = 0
                if ans < f[1]:
                    ans = f[1]
        return ans

Complexity

Pattern: Dynamic Programming

Define a state, write the transition, and stop recomputing the same subproblem. LeetCode 2272. Substring With Largest Variance 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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