New Problem Solution -"Largest Substring Between Two Equal Characters"

Author: haoel

README.md

@@ -50,6 +50,7 @@ LeetCode
 |1734|[Decode XORed Permutation](https://leetcode.com/problems/decode-xored-permutation/) | [C++](./algorithms/cpp/decodeXORedPermutation/DecodeXoredPermutation.cpp)|Medium|
 |1733|[Minimum Number of People to Teach](https://leetcode.com/problems/minimum-number-of-people-to-teach/) | [C++](./algorithms/cpp/minimumNumberOfPeopleToTeach/MinimumNumberOfPeopleToTeach.cpp)|Medium|
 |1732|[Find the Highest Altitude](https://leetcode.com/problems/find-the-highest-altitude/) | [C++](./algorithms/cpp/findTheHighestAltitude/FindTheHighestAltitude.cpp)|Easy|
+|1624|[Largest Substring Between Two Equal Characters](https://leetcode.com/problems/largest-substring-between-two-equal-characters/) | [C++](./algorithms/cpp/largestSubstringBetweenTwoEqualCharacters/LargestSubstringBetweenTwoEqualCharacters.cpp)|Easy|
 |1605|[Find Valid Matrix Given Row and Column Sums](https://leetcode.com/problems/find-valid-matrix-given-row-and-column-sums/) | [C++](./algorithms/cpp/FindValidMatrixGivenRowAndColumnSums/FindValidMatrixGivenRowAndColumnSums.cpp)|Medium|
 |1573|[Number of Ways to Split a String](https://leetcode.com/problems/number-of-ways-to-split-a-string/) | [C++](./algorithms/cpp/NumberOfWaysToSplitString/NumberOfWaysToSplitString.cpp)|Medium|
 |1556|[Thousand Separator](https://leetcode.com/problems/thousand-separator/) | [C++](./algorithms/cpp/thousandSeparator/ThousandSeparator.cpp)|Easy|

algorithms/cpp/largestSubstringBetweenTwoEqualCharacters/LargestSubstringBetweenTwoEqualCharacters.cpp

@@ -0,0 +1,56 @@
+// Source : https://leetcode.com/problems/largest-substring-between-two-equal-characters/
+// Author : Hao Chen
+// Date   : 2021-03-24
+
+/***************************************************************************************************** 
+ *
+ * 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.
+ ******************************************************************************************************/
+
+class Solution {
+public:
+    int maxLengthBetweenEqualCharacters(string s) {
+        int pos[26]={0};
+        
+        int longest = -1 ;
+        for (int i=0; i<s.size(); i++){
+            int idx = s[i] -'a';
+            if (pos[idx] == 0)  pos[idx] = i + 1; 
+            else longest = max(longest, i - pos[idx]);
+        }
+        
+        return longest;
+    }
+};