UniqueSubstringsinWraparoundString.java

package medium;

public class UniqueSubstringsinWraparoundString {
    /**A naive solution would definitely result in TLE.
     * Since the pattern keeps repeating, DP is the way to go.
     * Because the input consists merely of lowercase English letters, we could maintain an array of size 26,
     * keep updating this array, counting the substrings that end with this letter, keep updating it with the largest one possible.
     * 
     * Inspired by this: https://discuss.leetcode.com/topic/70658/concise-java-solution-using-dp*/
    public static int findSubstringInWraproundString(String p) {
        if (p == null || p.isEmpty()) return 0;
        if (p.length() < 2) return p.length();
        int count = 0;
        int[] dp = new int[26];
        dp[p.charAt(0) - 'a'] = 1;
        int len = 1;
        for (int i = 1; i < p.length(); i++) {
            if (p.charAt(i) - 1 == p.charAt(i-1) || (p.charAt(i) == 'a' && p.charAt(i-1) == 'z')){
                len++;
            } else {
                len = 1;
            }
            dp[p.charAt(i) - 'a'] = Math.max(len, dp[p.charAt(i) - 'a']);
        }
        
        for (int i : dp){
            count += i;
        }
        return count;
    }
    
    public static void main(String...args){
//        String p = "a";
//        String p = "abcgha";
        String p = "zab";
        System.out.println(findSubstringInWraproundString(p));
    }
}