Formatted question description: https://leetcode.ca/all/1624.html

# 1624. Largest Substring Between Two Equal Characters (Easy)

Given a string s, return the length of the longest substring between two equal characters, excluding the two characters. If there is no such substring return -1.

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

Example 1:

Input: s = "aa"
Output: 0
Explanation: The optimal substring here is an empty substring between the two 'a's.

Example 2:

Input: s = "abca"
Output: 2
Explanation: The optimal substring here is "bc".


Example 3:

Input: s = "cbzxy"
Output: -1
Explanation: There are no characters that appear twice in s.


Example 4:

Input: s = "cabbac"
Output: 4
Explanation: The optimal substring here is "abba". Other non-optimal substrings include "bb" and "".


Constraints:

• 1 <= s.length <= 300
• s contains only lowercase English letters.

Related Topics:
String

## Solution 1.

// OJ: https://leetcode.com/problems/largest-substring-between-two-equal-characters/

// Time: O(N)
// Space: O(1)
class Solution {
public:
int maxLengthBetweenEqualCharacters(string s) {
int ans = -1;
for (int i = 'a'; i <= 'z'; ++i) {
int first = -1, last = -1;
for (int j = 0; j < s.size(); ++j) {
if (s[j] != i) continue;
if (first == -1) first = j;
last = j;
}
ans = max(ans, last - first - 1);
}
return ans;
}
};


Java

class Solution {
public int maxLengthBetweenEqualCharacters(String s) {
int maxLength = -1;
Map<Character, Integer> map = new HashMap<Character, Integer>();
int length = s.length();
for (int i = 0; i < length; i++) {
char c = s.charAt(i);
if (map.containsKey(c)) {
int prevIndex = map.get(c);
maxLength = Math.max(maxLength, i - prevIndex - 1);
} else
map.put(c, i);
}
return maxLength;
}
}