https://leetcode.com/problems/count-number-of-homogenous-substrings/
Given a string s, return the number of homogenous substrings of s. Since the answer may be too large, return it modulo 109 + 7.
A string is homogenous if all the characters of the string are the same.
A substring is a contiguous sequence of characters within a string.
Example 1:
Input: s = "abbcccaa"
Output: 13
Explanation: The homogenous substrings are listed as below:
"a" appears 3 times.
"aa" appears 1 time.
"b" appears 2 times.
"bb" appears 1 time.
"c" appears 3 times.
"cc" appears 2 times.
"ccc" appears 1 time.
3 + 1 + 2 + 1 + 3 + 2 + 1 = 13.
Example 2:
Input: s = "xy"
Output: 2
Explanation: The homogenous substrings are "x" and "y".
Example 3:
Input: s = "zzzzz"
Output: 15
public class Solution
{
public int CountHomogenous(string s)
{
var homogenouses = new Dictionary<char, long>();
var usedSymbol = '\t';
var currentCount = 0;
for (var i = 0; i < s.Length; i++)
{
var currentSymbol = s[i];
if (currentSymbol.Equals(usedSymbol))
{
currentCount++;
if (homogenouses.TryGetValue(currentSymbol, out var usedCount))
homogenouses[currentSymbol] += currentCount;
else
homogenouses.Add(currentSymbol, 1);
}
else
{
currentCount = 1;
usedSymbol = currentSymbol;
if (homogenouses.ContainsKey(currentSymbol))
homogenouses[currentSymbol] += currentCount;
else
homogenouses.Add(currentSymbol, currentCount);
}
}
return (int)(homogenouses.Sum(x => x.Value) % 1000000007);
}
}