Leetcode-2272. Substring With Largest Variance [C++][Java]

目录

一、题目描述

二、解题思路

【C++】

【Java】

---

Leetcode-2272. Substring With Largest Variancehttps://leetcode.com/problems/substring-with-largest-variance/description/2272. 最大波动的子字符串 - 力扣（LeetCode）2272. 最大波动的子字符串 - 字符串的 波动 定义为子字符串中出现次数 最多 的字符次数与出现次数 最少 的字符次数之差。给你一个字符串 s ，它只包含小写英文字母。请你返回 s 里所有 子字符串的 最大波动 值。子字符串 是一个字符串的一段连续字符序列。 示例 1：输入：s = "aababbb"输出：3解释：所有可能的波动值和它们对应的子字符串如以下所示：- 波动值为 0 的子字符串："a" ，"aa" ，"ab" ，"abab" ，"aababb" ，"ba" ，"b" ，"bb" 和 "bbb" 。- 波动值为 1 的子字符串："aab" ，"aba" ，"abb" ，"aabab" ，"ababb" ，"aababbb" 和 "bab" 。- 波动值为 2 的子字符串："aaba" ，"ababbb" ，"abbb" 和 "babb" 。- 波动值为 3 的子字符串 "babbb" 。所以，最大可能波动值为 3 。示例 2：输入：s = "abcde"输出：0解释：s 中没有字母出现超过 1 次，所以 s 中每个子字符串的波动值都是 0 。 提示： * 1 <= s.length <= 104 * s  只包含小写英文字母。https://leetcode.cn/problems/substring-with-largest-variance/description/

一、题目描述

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.

二、解题思路

• 时间复杂度：O(n * 26)
• 空间复杂度：O(1)

【C++】

class Solution {
public:
    int largestVariance(string s) {
        int f0[26][26]{}, f1[26][26];
        memset(f1, -0x3f, sizeof(f1));
        int res = 0;
        for (auto& ch : s) {
            int a = ch - 'a';
            for (int b = 0; b < 26; ++b) {
                if (a == b) {continue;}
                f0[a][b] = max(f0[a][b], 0) + 1; // a为主频次（允许不含b）时的频次差
                f1[a][b]++; // a为主频次时的频次差，含b时有效；不含b时为很小的负数值
                f1[b][a] = f0[b][a] = max(f0[b][a], 0) - 1; // b为主频次（这里一定含a）时的频次差
                res = max(max(res, f1[a][b]), f1[b][a]);
            }
        }
        return res;
    }
};

【Java】

class Solution {
    public int largestVariance(String s) {
        int f0[][] = new int[26][26], f1[][] = new int[26][26];
        for (int[] row : f1) {Arrays.fill(row, Integer.MIN_VALUE);}
        int res = 0;
        for (char ch : s.toCharArray()) {
            int a = ch - 'a';
            for (int b = 0; b < 26; ++b) {
                if (a == b) {continue;}
                f0[a][b] = Math.max(f0[a][b], 0) + 1;
                f1[a][b]++;
                f1[b][a] = f0[b][a] = Math.max(f0[b][a], 0) - 1;
                res = Math.max(Math.max(res, f1[a][b]), f1[b][a]);
            }
        }
        return res;
    }
}