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647. Palindromic Substrings
Medium
Given a string s, return the number of palindromic substrings in it.
A string is a palindrome when it reads the same backward as forward.
A substring is a contiguous sequence of characters within the string.
Example 1:
Input: s = “abc”
Output: 3
Explanation: Three palindromic strings: “a”, “b”, “c”.
Example 2:
Input: s = “aaa”
Output: 6
Explanation: Six palindromic strings: “a”, “a”, “a”, “aa”, “aa”, “aaa”.
Constraints:
1 <= s.length <= 1000sconsists of lowercase English letters.
Solution
public class Solution {
private void Expand(char[] a, int l, int r, int[] res) {
while (l >= 0 && r < a.Length) {
if (a[l] != a[r]) {
return;
} else {
res[0]++;
l--;
r++;
}
}
}
public int CountSubstrings(string s) {
char[] a = s.ToCharArray();
int[] res = {0};
for (int i = 0; i < a.Length; i++) {
Expand(a, i, i, res);
Expand(a, i, i + 1, res);
}
return res[0];
}
}