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
func expand(a []rune, l int, r int, res *int) {
for l >= 0 && r < len(a) {
if a[l] != a[r] {
return
} else {
*res++
l--
r++
}
}
}
func countSubstrings(s string) int {
a := []rune(s)
res := 0
for i := 0; i < len(a); i++ {
expand(a, i, i, &res)
expand(a, i, i+1, &res)
}
return res
}