剑指-020

class Solution {
    public int countSubstrings(String s) {
        int len = s.length();
        int count = 0;
        for(int i = 0; i < len * 2 - 1; i++){
            int left = i/2;
            int right = i/2 + i%2;
            while(left >= 0 && right <= len - 1 && s.charAt(left) == s.charAt(right)){
                left--;
                right++;
                count++;
            }
        }
        return count;
    }
}
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