Substrings That Begin and End With the Same Letter

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Problem Description

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Solutions

Solution 1: C# (Best: 76 ms)

Metric	Value
Runtime	76 ms
Memory	40.7 MB
Date	2021-12-29

Solution

public class Solution {
    public long NumberOfSubstrings(string s) {
      long n = s.Length;
    long count = 0;
    long[] occurences = new long[26];
    for (int i = 0; i < n; i++)
    {
        occurences[s[i] - 'a'] += 1;
    }
    for (int i = 0; i < 26; i++)
    {
        count += occurences[i] > 0 ? (occurences[i] * (occurences[i] + 1)) / 2 : 0;
    }

    return count;
    }
}

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Complexity Analysis

Approach	Time	Space
Solution	To be analyzed	To be analyzed