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