647. Palindromic Substrings

Problem

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 <= 1000

• s consists of lowercase English letters.

Solution

/**
 * @param {string} s
 * @return {number}
 */
var countSubstrings = function(s) {
    let count = 0;
    for (let i = 0; i < s.length; i ++) {
        for (let j = i; j < i + 2; j ++) {
            let left = i;
            let right = j;
            while (left >= 0 && right < s.length && s[left] === s[right]) {
                count ++;
                left --;
                right ++;
            }
        }
    }
    return count;
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).