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path: root/2022/day09/main2.c
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#include <stdio.h>
#include <stdlib.h>

typedef struct Cord_ Cord;

typedef struct Cord_ {
    int x,y;
    Cord *next, *prev;
} Cord;

Cord* updateTail(Cord *head, Cord *tail)
{
    int dy, dx, d;
    dx = head->x - tail->x;
    dy = head->y - tail->y;
    d = dx * dx + dy * dy;
    // distance <= 1
    if ( d <= 2) return tail;
    tail->x += (dx + dx/abs(dx))/2;
    tail->y += (dy + dy/abs(dy))/2;

    return tail;
}

int main()
{
    char c;
    int d;
    Cord h[10] = {0};
    while (scanf("%c %d\n", &c, &d) != EOF)
    {
        printf("%c %d\n", c, d);
        for (int i = 0; i < d; i++)
        {
            h[0].x += (c == 'R') - (c == 'L');
            h[0].y += (c == 'U') - (c == 'D');
            printf("H %d %d \n", h->x, h->y);
            for (int i = 0; i < 9; i++)
            {
                updateTail(&h[i], &h[i+1]);
            }
            printf("T %d %d \n", h[9].x, h[9].y);
        }
    }

}

// ./main < input2.txt | grep T | sort | uniq | wc -l