76. Minimum Window Substring

Author: benjiwright

csharp/76-Minimum-Window-Substring.cs

@@ -0,0 +1,60 @@
+public class Solution
+{
+
+    public string MinWindow(string s, string t)
+
+    {
+        if (string.IsNullOrEmpty(t)) return string.Empty;
+
+        var countT = new Dictionary<char, int>();
+        var window = new Dictionary<char, int>();
+
+        foreach (var c in t)
+        {
+            AddCharToDictionary(c, countT);
+        }
+
+        var have = 0;
+        var need = countT.Count;
+        var left = 0;
+        var res = new[] { -1, -1 };
+        var resultLength = int.MaxValue;
+        for (var right = 0; right < s.Length; right++)
+        {
+            var c = s[right];
+            AddCharToDictionary(c, window);
+
+            if (countT.ContainsKey(c) && window[c] == countT[c]) have++;
+
+            while (have == need)
+            {
+                // update our result
+                var windowSize = right - left + 1;
+                if (windowSize < resultLength)
+                {
+                    res = new[] { left, right };
+                    resultLength = windowSize;
+                }
+
+                // pop from the left of our window
+                window[s[left]]--;
+                if (countT.ContainsKey(s[left]) && window[s[left]] < countT[s[left]])
+                {
+                    have--;
+                }
+
+                left++;
+            }
+        }
+
+        return resultLength == int.MaxValue
+           ? string.Empty
+           : s.Substring(res[0], res[1] - res[0] + 1);
+    }
+
+    private void AddCharToDictionary(char c, IDictionary<char, int> dict)
+    {
+        if (dict.ContainsKey(c)) dict[c]++;
+        else dict.Add(c, 1);
+    }
+}