Substring [Swift] LeetCode1180 statistics contain only a single letter |. Count Substrings with Only One Distinct Letter

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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.

---

 

Give you a string  S, it returns the number of sub-strings contain only a single letter.

Example 1:

Input: "aaaba" 
Output: 8 
Explanation: 
containing only a single sub-string are letters "aaa", "aa", "a", "b". 
"aaa" appear more than once. 
"aa" appears twice. 
"a" appears 4 times. 
"b" appear more than once. 
So the answer is 1 + 2 + 4 + 1 = 8.

Example 2:

Enter: "aaaaaaaaaa" 
Output: 55

 

prompt:

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

---

 

Runtime: 4 ms

Memory Usage: 21 MB

 1 class Solution {
 2     func countLetters(_ S: String) -> Int {
 3         var arr:[Character] = Array(S)
 4         arr.append("#")
 5         var k:Int = 0
 6         var c:Character = "#"
 7         var ans:Int = 0
 8         for i in 0..<arr.count
 9         {
10             if arr[i] == c
11             {
12                 k += 1
13             }
14             else
15             {
16                 if c != "#"
17                 {
18                     ans += k * (k + 1) / 2
19                 }
20                 c = arr[i]
21                 k = 1
22             }
23         }
24         return ans
25     }
26 }