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copied!<p><strong>Table lookup</strong></p> <pre><code>#include <stdio.h> #define SIZE 16 #define SIDE 4 //sqrt(SIZE) int table[SIZE]; int rtable[100];// {x,y| x<=99, y<=99 } void setup(){ int i, x, y, xy, index;//xy = x + y x=y=xy=0; for(i=0;i<SIZE;++i){ table[i]= index= x*10 + y; rtable[x*10+y]=i; x = x + 1; y = y - 1;//right up if(y < 0 || x >= SIDE){ ++xy; x = 0; y = xy;; while(y>=SIDE){ ++x; --y; } } } } int getNGonalNeighbor(int index, int offsetX, int offsetY){ int x,y; x=table[index] / 10 + offsetX; y=table[index] % 10 + offsetY; if(x < 0 || x >= SIDE || y < 0 || y >= SIDE) return -1; //ERROR return rtable[ x*10+y ]; } int main() { int i; setup(); printf("%d\n", getNGonalNeighbor(15,-1,-1)); printf("%d\n", getNGonalNeighbor(15, 0,-1)); printf("%d\n", getNGonalNeighbor(15,-1, 0)); printf("%d\n", getNGonalNeighbor(11,-2,-1)); printf("%d\n", getNGonalNeighbor(0, -1,-1)); return 0; } </code></pre> <p>don't use table version.</p> <pre><code>#include <stdio.h> #define SIZE 16 #define SIDE 4 void num2xy(int index, int *offsetX, int *offsetY){ int i, x, y, xy;//xy = x + y x=y=xy=0; for(i=0;i<SIZE;++i){ if(i == index){ *offsetX = x; *offsetY = y; return; } x = x + 1; y = y - 1;//right up if(y < 0 || x >= SIDE){ ++xy; x = 0; y = xy;; while(y>=SIDE){ ++x; --y; } } } } int xy2num(int offsetX, int offsetY){ int i, x, y, xy, index;//xy = x + y x=y=xy=0; for(i=0;i<SIZE;++i){ if(offsetX == x && offsetY == y) return i; x = x + 1; y = y - 1;//right up if(y < 0 || x >= SIDE){ ++xy; x = 0; y = xy;; while(y>=SIDE){ ++x; --y; } } } return -1; } int getNGonalNeighbor(int index, int offsetX, int offsetY){ int x,y; num2xy(index, &x, &y); return xy2num(x + offsetX, y + offsetY); } int main() { printf("%d\n", getNGonalNeighbor(15,-1,-1)); printf("%d\n", getNGonalNeighbor(15, 0,-1)); printf("%d\n", getNGonalNeighbor(15,-1, 0)); printf("%d\n", getNGonalNeighbor(11,-2,-1)); printf("%d\n", getNGonalNeighbor(0, -1,-1)); return 0; } </code></pre>

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