leetcode 1180. Count Substrings with Only One Distinct Letter

Seawolf

Given a string S, return the number of substrings that have only one distinct letter.

 

Example 1:

Input: S = "aaaba"
Output: 8
Explanation: The substrings with one distinct letter are "aaa", "aa", "a", "b".
"aaa" occurs 1 time.
"aa" occurs 2 times.
"a" occurs 4 times.
"b" occurs 1 time.
So the answer is 1 + 2 + 4 + 1 = 8.
Example 2:

Input: S = "aaaaaaaaaa"
Output: 55
 

Constraints:

1 <= S.length <= 1000
S[i] consists of only lowercase English letters.

class Solution {
    public int countLetters(String S) {
        if (S.length() == 0) return 0;
        if (S.length() == 1) return 1;
        int sum = 0;
        String remain = "";
        Set <String> set = new HashSet<>();
        String init = S.substring(0,1);
        set.add(init);
        for(int i = 0; i< S.length(); i++){
            
            if(S.substring(i,i+1).equals(init)) {
                
                remain = remain + S.substring(i,i+1);
                set.add(remain + S.substring(i,i+1));
            }
            else {
                remain = "";
                init = S.substring(i,i+1);
                
                set.add(init);
            }
        }
        Iterator<String> iterator = set.iterator();
        while(iterator.hasNext()) {
            sum = sum + compare(S,iterator.next());
        }
        
        return sum;
    }
    
    public int compare(String S, String s){
        int sum = 0;
        for(int i = 0; i<= S.length() - s.length(); i++){
            if(S.substring(i,i+s.length()).equals(s)) sum ++;
            
        }
        return sum;
    }
}