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
object Solution {
private def expand(a: Array[Char], l: Int, r: Int, res: Array[Int]): Unit = {
var left = l
var right = r
while (left >= 0 && right < a.length) {
if (a(left) != a(right)) {
return
} else {
res(0) += 1
left -= 1
right += 1
}
}
}
def countSubstrings(s: String): Int = {
val a = s.toCharArray
val res = Array(0)
for (i <- 0 until a.length) {
expand(a, i, i, res)
expand(a, i, i + 1, res)
}
res(0)
}
}