Palindromic Substrings

class Solution {
public:
    int countSubstrings(string s) {
        int count = 0;
        for (int center = 0; center < (int)s.size(); ++center) {
            count += expand(s, center, center);
            count += expand(s, center, center + 1);
        }
        return count;
    }
private:
    int expand(const string& s, int l, int r) {
        int n = 0;
        while (l >= 0 && r < (int)s.size() && s[l] == s[r]) { ++n; --l; ++r; }
        return n;
    }
};

func countSubstrings(s string) int {
    expand := func(l, r int) int {
        n := 0
        for l >= 0 && r < len(s) && s[l] == s[r] {
            n++
            l--
            r++
        }
        return n
    }
    count := 0
    for center := 0; center < len(s); center++ {
        count += expand(center, center)
        count += expand(center, center+1)
    }
    return count
}

class Solution:
    def countSubstrings(self, s: str) -> int:
        def expand(l: int, r: int) -> int:
            n = 0
            while l >= 0 and r < len(s) and s[l] == s[r]:
                n += 1
                l -= 1
                r += 1
            return n

        count = 0
        for center in range(len(s)):
            count += expand(center, center)
            count += expand(center, center + 1)
        return count

function countSubstrings(s) {
    const expand = (l, r) => {
        let n = 0;
        while (l >= 0 && r < s.length && s[l] === s[r]) {
            n++;
            l--;
            r++;
        }
        return n;
    };
    let count = 0;
    for (let center = 0; center < s.length; center++) {
        count += expand(center, center);
        count += expand(center, center + 1);
    }
    return count;
}

class Solution {
    private String s;

    public int countSubstrings(String s) {
        this.s = s;
        int count = 0;
        for (int center = 0; center < s.length(); center++) {
            count += expand(center, center);
            count += expand(center, center + 1);
        }
        return count;
    }

    private int expand(int l, int r) {
        int n = 0;
        while (l >= 0 && r < s.length() && s.charAt(l) == s.charAt(r)) {
            n++;
            l--;
            r++;
        }
        return n;
    }
}

function countSubstrings(s: string): number {
    const expand = (l: number, r: number): number => {
        let n = 0;
        while (l >= 0 && r < s.length && s[l] === s[r]) {
            n++;
            l--;
            r++;
        }
        return n;
    };
    let count = 0;
    for (let center = 0; center < s.length; center++) {
        count += expand(center, center);
        count += expand(center, center + 1);
    }
    return count;
}