From d2b55bc17b5aef1409977840582a4cfdac848532 Mon Sep 17 00:00:00 2001
From: Matej Focko <me@mfocko.xyz>
Date: Sat, 5 Oct 2024 23:35:43 +0200
Subject: [PATCH] =?UTF-8?q?cs:=20add=20=C2=AB567.=20Permutation=20in=20Str?=
 =?UTF-8?q?ing=C2=BB?=
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Signed-off-by: Matej Focko <me@mfocko.xyz>
---
 cs/permutation-in-string.cs | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 cs/permutation-in-string.cs

diff --git a/cs/permutation-in-string.cs b/cs/permutation-in-string.cs
new file mode 100644
index 0000000..9c79542
--- /dev/null
+++ b/cs/permutation-in-string.cs
@@ -0,0 +1,36 @@
+public class Solution {
+    private int[] GetFreqs(string s, int begin, int end) {
+        var freqs = new int[26];
+
+        for (int i = begin; i < end; ++i) {
+            ++freqs[s[i] - 'a'];
+        }
+
+        return freqs;
+    }
+    private int[] GetFreqs(string s) => GetFreqs(s, 0, s.Length);
+
+    public bool CheckInclusion(string s1, string s2) {
+        if (s2.Length < s1.Length) {
+            return false;
+        }
+
+        var expected = GetFreqs(s1);
+
+        var running = GetFreqs(s2, 0, s1.Length);
+        if (Enumerable.SequenceEqual(running, expected)) {
+            return true;
+        }
+
+        for (int i = s1.Length; i < s2.Length; ++i) {
+            --running[s2[i - s1.Length] - 'a'];
+            ++running[s2[i] - 'a'];
+
+            if (Enumerable.SequenceEqual(running, expected)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}