Create 0076-minimum-window-substring.swift

Author: AyselHeydarova

0076-minimum-window-substring.swift

@@ -0,0 +1,51 @@
+class Solution {
+    func minWindow(_ s: String, _ t: String) -> String {
+    if t.isEmpty  { return "" }
+
+        var countT: [Character : Int] = [:]
+        var window: [Character : Int] = [:]
+        let stringArray = Array(s)
+
+        // Storing each char and its count in hashMap
+        for char in t {
+            countT[char, default: 0] += 1
+        }
+
+        var have = 0
+        let need = t.count
+        var resultRange = (-1, -1)
+        var resultLength = Int.max
+        var l = 0
+
+        for r in 0...s.count - 1 {
+            let char = stringArray[r]
+            window[char, default: 0] += 1
+
+            if countT.contains(where: { $0.key == char }) && window[char] == countT[char] {
+            // for the case of repeated characters "have" should be increased by count, not by 1
+                have += countT[char, default: 0]
+            }
+
+            while have == need {
+                // update result
+                if r - l + 1 < resultLength {
+                    resultRange = (l, r)
+                    resultLength  = r - l + 1
+                }
+                // pop from left of the window
+                window[stringArray[l], default: 0] -= 1
+
+                if countT.contains(where: { $0.key == stringArray[l] })
+                    && window[stringArray[l], default: 0] < countT[stringArray[l], default: 0] {
+                    //subtract all count, because in second iteration will be added total count of char.
+                    have -= countT[stringArray[l], default: 0]
+                }
+
+                l += 1
+            }
+        }
+
+        guard resultLength != Int.max else { return "" }
+        return String(stringArray[resultRange.0...resultRange.1])
+    }
+}