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// @Title: 回文子字符串的个数 (回文子字符串的个数)
// @Author: 15816537946@163.com
// @Date: 2022-03-23 23:29:43
// @Runtime: 0 ms
// @Memory: 1.9 MB
func countSubstrings(s string) int {
    n := len(s)
    if n == 0 {
        return 0 
    }

    var ret int 
    var subString func(int, int)
    subString = func(lo, hi int) {
        for lo >= 0 && hi < n && s[lo] == s[hi] {
            ret++
            lo--
            hi++
        }
    }
    
    for i := range s {
        subString(i, i)
        subString(i, i+1)
    }
    return ret
}