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  • 2.1.5 Hamming Codes

    Hamming Codes
    Rob Kolstad

    Given N, B, and D: Find a set of N codewords (1 <= N <= 64), each of length B bits (1 <= B <= 8), such that each of the codewords is at least Hamming distance of D (1 <= D <= 7) away from each of the other codewords. The Hamming distance between a pair of codewords is the number of binary bits that differ in their binary notation. Consider the two codewords 0x554 and 0x234 and their differences (0x554 means the hexadecimal number with hex digits 5, 5, and 4):

            0x554 = 0101 0101 0100
            0x234 = 0010 0011 0100
    Bit differences: xxx  xx
    

    Since five bits were different, the Hamming distance is 5.

    PROGRAM NAME: hamming

    INPUT FORMAT

    N, B, D on a single line

    SAMPLE INPUT (file hamming.in)

    16 7 3
    

    OUTPUT FORMAT

    N codewords, sorted, in decimal, ten per line. In the case of multiple solutions, your program should output the solution which, if interpreted as a base 2^B integer, would have the least value.

    SAMPLE OUTPUT (file hamming.out)

    0 7 25 30 42 45 51 52 75 76
    82 85 97 102 120 127
    
    {
    ID: makeeca1
    PROG: hamming
    LANG: PASCAL
    }
    var N,B,D,i,j:longint;bool:boolean;
        f:array[0..100]of longint;
    function work(x:longint):boolean;
    var i:longint;
    begin
      i:=0;
      while x>0 do begin if x and 1=1 then inc(i);x:=x>>1;end;
      if i>=d then exit(true);exit(false);
    end;
    begin
      assign(input,'hamming.in');reset(input);
      assign(output,'hamming.out');rewrite(output);
      readln(N,B,D);close(input);
      fillchar(f,sizeof(f),0);f[0]:=1;
      repeat
        inc(i);bool:=true;
        for j:=1 to f[0]do
          bool:=bool and (work(i xor f[j]));
        if bool then begin inc(f[0]);f[f[0]]:=i;end;
      until f[0]=N;
      for i:=1 to N-1 do
      begin
        write(f[i]);
        if i mod 10=0 then writeln else write(' ');
      end;
      writeln(f[N]);
      close(output);
    end.
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  • 原文地址:https://www.cnblogs.com/makeecat/p/3274559.html
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