LeetCode-in-All
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
class Solution {
private fun expand(a: CharArray, l: Int, r: Int, res: IntArray) {
var left = l
var right = r
while (left >= 0 && right < a.size) {
if (a[left] != a[right]) {
return
} else {
res[0]++
left--
right++
}
}
}
fun countSubstrings(s: String): Int {
val a = s.toCharArray()
val res = intArrayOf(0)
for (i in a.indices) {
expand(a, i, i, res)
expand(a, i, i + 1, res)
}
return res[0]
}
}