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Assets/BitWise.cs

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+using System.Collections.Generic;
+
+public class BitWise
+{
+    public static int HammingWeight(long x)
+    {
+        const long h01 = 0x0101010101010101;
+        const long m1 = 0x5555555555555555; // 0101...
+        const long m2 = 0x3333333333333333; // 00110011..
+        const long m4 = 0x0f0f0f0f0f0f0f0f;
+        x -= (x >> 1) & m1;             // put count of each 2 bits into those 2 bits
+        x = (x & m2) + ((x >> 2) & m2); // put count of each 4 bits into those 4 bits
+        x = (x + (x >> 4)) & m4;        // put count of each 8 bits into those 8 bits
+        return (int)((x * h01) >> 56);
+    }
+
+    /// <summary>
+    /// return all the permutation of n choose p, long output are bitflags were 1 bit represent selected.
+    /// Exactly n bits are set to 1, among the p first bits.
+    /// n parmi p
+    /// </summary>
+    /// <param name="totalNumberOfElement"></param>
+    /// <param name="numberOfElementToSelect"></param>
+    /// <returns></returns>
+    public static HashSet<long> GetAllPermutation(int numberOfElementToSelect, int totalNumberOfElement)
+    {
+        HashSet<long> result = new HashSet<long>();
+        if (numberOfElementToSelect>totalNumberOfElement)
+        {
+            return result;
+        }
+
+        long v = (1L << numberOfElementToSelect) - 1;
+        long end = 1L << totalNumberOfElement;
+        while (v < end)
+        {
+            result.Add(v);
+            long t = (v | (v - 1)) + 1;
+            v = t | ((((t & -t) / (v & -v)) >> 1) - 1);
+        }
+
+        return result;
+    }
+}