201 Bitwise AND of Numbers Range

Author: Kai Yang

201.BitwiseAndOfNumbersRange.Test.cs

@@ -0,0 +1,28 @@
+using System;
+using NUnit.Framework;
+
+[TestFixture]
+public class TestClass : TestClassBase
+{
+    [TestCase(100, 1000)]
+    public void TestMethod(int maxDiff, int repeatTimes)
+    {
+        Repeat(repeatTimes, () =>
+        {
+           var m = Random.Next();
+           var n = m + Math.Min(int.MaxValue - m, Random.Next(maxDiff));
+           var expectedResult = RangeBitwiseAnd(m, n);
+           var result = new Solution().RangeBitwiseAnd(m, n);
+           Assert.AreEqual(expectedResult, result, "m: {0}. n: {1}.", m, n);
+        });
+    }
+
+    private int RangeBitwiseAnd(int m, int n) {
+        var result = m;
+        for (var i = m + 1; i <= n; ++i)
+        {
+            result &= i;
+        }
+        return result;
+    }
+}

201.BitwiseAndOfNumbersRange.cs

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+public class Solution {
+    public int RangeBitwiseAnd(int m, int n) {
+        var and = m & n;
+        var xor = m ^ n;
+        var temp = 0;
+        while (xor > 0)
+        {
+            temp = (temp << 1) + 1;
+            xor >>= 1;
+        }
+        return and & (~temp);
+    }
+}