LeetCode-647. Palindromic Substrings [C++][Java]

LeetCode-647. Palindromic Substringshttps://leetcode.com/problems/palindromic-substrings/

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.

class Solution {
public:
    int countSubstrings(string s) {
        int count = 0;
        for (int i = 0; i < s.length(); ++i) {
            count += extendSubstrings(s, i, i); // 奇数长度
            count += extendSubstrings(s, i, i + 1); // 偶数长度
        }
        return count;
    }
    
    int extendSubstrings(string s, int l, int r) {
        int count = 0;
        while (l >= 0 && r < s.length() && s[l] == s[r]) {
            --l;
            ++r;
            ++count;
        }
        return count;
    }
};

class Solution {
    public int countSubstrings(String s) {
        int count = 0;
        for (int i = 0; i < s.length(); ++i) {
            count += extendSubstrings(s, i, i); // 奇数长度
            count += extendSubstrings(s, i, i + 1); // 偶数长度
        }
        return count;
    }
    
    int extendSubstrings(String s, int l, int r) {
        int count = 0;
        while (l >= 0 && r < s.length() && s.charAt(l) == s.charAt(r)) {
            --l;
            ++r;
            ++count;
        }
        return count;
    }
}