Count Binary Substrings.

Author: recherst

Easy/696.Count Binary Substrings.playground/Contents.swift

@@ -0,0 +1,54 @@
+/**
+ Given a binary string s, return the number of non-empty substrings that have the same number of 0's and 1's, and all the 0's and all the 1's in these substrings are grouped consecutively.
+
+ Substrings that occur multiple times are counted the number of times they occur.
+
+  
+
+ Example 1:
+ Input: s = "00110011"
+ Output: 6
+ Explanation: There are 6 substrings that have equal number of consecutive 1's and 0's: "0011", "01", "1100", "10", "0011", and "01".
+ Notice that some of these substrings repeat and are counted the number of times they occur.
+ Also, "00110011" is not a valid substring because all the 0's (and 1's) are not grouped together.
+ 
+ Example 2:
+ Input: s = "10101"
+ Output: 4
+ Explanation: There are 4 substrings: "10", "01", "10", "01" that have equal number of consecutive 1's and 0's.
+  
+
+ Constraints:
+ - 1 <= s.length <= 105
+ - s[i] is either '0' or '1'.
+ */
+class Solution {
+    func countBinarySubstrings(_ s: String) -> Int {
+        var arr = [String(s.first!)]
+        for (i, c) in s.enumerated() {
+            if i > 0 {
+                let character = arr.last!.last!
+                if c == character {
+                    var element = arr.popLast()!
+                    element.append("\(c)")
+                    arr.append(element)
+                } else {
+                    arr.append("\(c)")
+                }
+            }
+        }
+        
+        var totalCount = 0
+        for (i, e) in arr.enumerated() {
+            if i < arr.count - 1 {
+                let lastElement = arr[i + 1]
+                totalCount += e.count >= lastElement.count ? lastElement.count : e.count
+            }
+        }
+        return totalCount
+    }
+}
+
+let s = Solution()
+let r = s.countBinarySubstrings("11110011")
+print(r)

Easy/696.Count Binary Substrings.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios' buildActiveScheme='true' importAppTypes='true'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Easy/696.Count Binary Substrings.playground/playground.xcworkspace/contents.xcworkspacedata

@@ -124,6 +124,7 @@
 120. [Valid Palindrome II](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/680.Valid%20Palindrome%20II.playground/Contents.swift)
 121. [Baseball Game](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/682.Baseball%20Game.playground/Contents.swift)
 122. [Binary Number with Alternating Bits](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/693.Binary%20Number%20with%20Alternating%20Bits.playground/Contents.swift)
+123. [Count Binary Substrings](https://github.com/recherst/leetcode-algtorithm/blob/main/Easy/696.Count%20Binary%20Substringsplayground/Contents.swift)
 
 #### Medium