/*** 2d random work program by uniform random number ***/
/*** K.S, KU, 2025/7/3 ***/
#include	<stdio.h>
#include	<stdlib.h> /* for random function parameter */
#define	NR	100000
main()
{
	int	rx, ry, ixy[NR][NR], rxmin, rxmax, rymin, rymax;
	int	i, j, nstep = 10000;
	int	ir;
	FILE	*fp;
	rxmin = -500; rxmax = 500;
	rymin = -500; rymax = 500;
	for (i = rxmin; i <= rxmax; i++) {
		for (j = rymin; j <= rymax; j++) ixy[i-rxmin][j-rymin] = 0;
	}

	/* open trajectory file */
	fp = fopen("xytrajectory.dat", "w");

	rx = 0;
	ry = 0;
	for (i = 0; i < nstep; i++) {
		ir = rand();	/* built-in random number generator */
			/* (rand() will generate between [0,RAND_MAX)) */
				/* RAND_MAX is system-built-in parameter  */
		if ((double)ir / RAND_MAX < 0.25) { 
			rx--;  /* left: -x  */
		} else if ((double)ir / RAND_MAX >= 0.25 
			&& (double)ir / RAND_MAX < 0.50) {
			rx++;  /* right:+x */
		} else if ((double)ir / RAND_MAX >= 0.50 
			&& (double)ir / RAND_MAX < 0.75) { 
			ry--;  /* down: -y */
		} else if ((double)ir / RAND_MAX >= 0.75) {
			ry++;  /* up:   +y */
		}
		ixy[rx-rxmin][ry-rymin]++;
		/* fprintf(stderr, "%d %d %d\n", i, rx, ry); */
		fprintf(fp, "%d %d %d\n", i, rx, ry);
	}
	fclose(fp);
	for (i = rxmin; i <= rxmax; i++) {
		for (j = rymin; j <= rymax; j++) 
			if(ixy[i-rxmin][j-rymin] != 0)
				printf("%5d %5d %5d\n", 
					i, j, ixy[i-rxmin][j-rymin]);
	}
}