Code Golf: Tic Tac Toe

Answer 1

c -- 144 characters

Minified:

#define A(x) a[b[x%16]]
int c,b[]={4,8,0,1,2,4,6,0,3,4,5,2,8,6,7,2};int
T(int*a){for(c=0;c<16;c+=2)if(A(c)&A(c+1)&A(c+2))return A(c);return 0;}

Both returns count (one necessary and the other would need replacing with a space).

The array codes for the eight ways to win in triplets starting from even positions and taken mod 16.

Bitwise and trick stolen from Eric Pi.

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More readable form:

#define A(x) a[b[x%16]]

// Compact coding of the ways to win.
//
// Each possible was starts a position N*2 and runs through N*2+2 all
// taken mod 16
int c,b[]={4,8,0,1,2,4,6,0,3,4,5,2,8,6,7,2};

int T(int*a){
  // Loop over the ways to win
  for(c=0;c<16;c+=2)
    // Test for a win
    if(A(c)&A(c+1)&A(c+2))return A(c);
  return 0;
}

Testing scaffold:

#include 
#include 

int T(int*);

int main(int argc, char**argv){
  int input[9]={0};
  int i, j;
  for (i=1; i