2272. Substring With Largest Variance

Description

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.

Given a string s consisting of lowercase English letters only, return the largest variance possible among all substrings of s.

A substring is a contiguous sequence of characters within a string.

 

Example 1:

Input: s = "aababbb"
Output: 3
Explanation:
All possible variances along with their respective substrings are listed below:
- Variance 0 for substrings "a", "aa", "ab", "abab", "aababb", "ba", "b", "bb", and "bbb".
- Variance 1 for substrings "aab", "aba", "abb", "aabab", "ababb", "aababbb", and "bab".
- Variance 2 for substrings "aaba", "ababbb", "abbb", and "babb".
- Variance 3 for substring "babbb".
Since the largest possible variance is 3, we return it.

Example 2:

Input: s = "abcde"
Output: 0
Explanation:
No letter occurs more than once in s, so the variance of every substring is 0.

 

Constraints:

  • 1 <= s.length <= 104
  • s consists of lowercase English letters.

Solutions

Solution 1

Python Code
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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

Java Code
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class Solution {
    public int largestVariance(String s) {
        int n = s.length();
        int ans = 0;
        for (char a = 'a'; a <= 'z'; ++a) {
            for (char b = 'a'; b <= 'z'; ++b) {
                if (a == b) {
                    continue;
                }
                int[] f = new int[] {0, -n};
                for (int i = 0; i < n; ++i) {
                    if (s.charAt(i) == a) {
                        f[0]++;
                        f[1]++;
                    } else if (s.charAt(i) == b) {
                        f[1] = Math.max(f[0] - 1, f[1] - 1);
                        f[0] = 0;
                    }
                    ans = Math.max(ans, f[1]);
                }
            }
        }
        return ans;
    }
}

C++ Code
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class Solution {
public:
    int largestVariance(string s) {
        int n = s.size();
        int ans = 0;
        for (char a = 'a'; a <= 'z'; ++a) {
            for (char b = 'a'; b <= 'z'; ++b) {
                if (a == b) continue;
                int f[2] = {0, -n};
                for (char c : s) {
                    if (c == a) {
                        f[0]++;
                        f[1]++;
                    } else if (c == b) {
                        f[1] = max(f[1] - 1, f[0] - 1);
                        f[0] = 0;
                    }
                    ans = max(ans, f[1]);
                }
            }
        }
        return ans;
    }
};

Go Code
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func largestVariance(s string) int {
	ans, n := 0, len(s)
	for a := 'a'; a <= 'z'; a++ {
		for b := 'a'; b <= 'z'; b++ {
			if a == b {
				continue
			}
			f := [2]int{0, -n}
			for _, c := range s {
				if c == a {
					f[0]++
					f[1]++
				} else if c == b {
					f[1] = max(f[1]-1, f[0]-1)
					f[0] = 0
				}
				ans = max(ans, f[1])
			}
		}
	}
	return ans
}