LeetCode-in-Java
3084. Count Substrings Starting and Ending with Given Character
Medium
You are given a string s and a character c. Return the total number of substrings of s that start and end with c.
Example 1:
Input: s = “abada”, c = “a”
Output: 6
Explanation: Substrings starting and ending with "a" are: "**a**bada", "**aba**da", "**abada**", "ab**a**da", "ab**ada**", "abad**a**".
Example 2:
Input: s = “zzz”, c = “z”
Output: 6
Explanation: There are a total of 6 substrings in s and all start and end with "z".
Constraints:
1 <= s.length <= 105sandcconsist only of lowercase English letters.
Solution
public class Solution {
public long countSubstrings(String s, char c) {
long count = 0;
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == c) {
count++;
}
}
return (count * (count + 1)) / 2;
}
}