Day 1: Typing, Donut & LeetCode

1. Warm-Up: Typing Practice

Improve your typing speed and accuracy here: Typeracer

2. Core Challenge: Spinning Donut in C


#include <math.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

int main() {
    float A = 0, B = 0, i, j;
    const float R1 = 1;      // inner radius
    const float R2 = 2;      // outer radius
    const float K2 = 5;      // distance from viewer to donut center

    // Terminal size
    const int width  = 80;
    const int height = 24;

    // Scaling factor: lower K1 → smaller donut
    const float K1 = width * K2 * 3 / (16 * (R1 + R2));

    float z[width * height];
    char  b[width * height + 1];
    b[width*height] = '\0';

    while (1) {
        memset(b, ' ', width * height);
        memset(z, 0, sizeof(z));

        for (j = 0; j < 2 * M_PI; j += 0.07) {
            for (i = 0; i < 2 * M_PI; i += 0.02) {
                float cosj = cosf(j), sinj = sinf(j);
                float cosi = cosf(i), sini = sinf(i);
                float cosA = cosf(A), sinA = sinf(A);
                float cosB = cosf(B), sinB = sinf(B);

                float circlex = R2 + R1 * cosi;
                float circley = R1 * sini;

                float x = circlex * (cosB * cosj + sinA * sinB * sinj)
                        - circley * cosA * sinB;
                float y = circlex * (sinB * cosj - sinA * cosB * sinj)
                        + circley * cosA * cosB;
                float zval = circlex * (cosA * cosj * sinB - sinA * sinj)
                           + circley * sinA * cosj
                           + K2;

                float ooz = 1.0f / zval;

                int xp = (int)(width  / 2 + K1 * ooz * x);
                int yp = (int)(height / 2 - K1 * ooz * y);
                int idx = xp + yp * width;

                float L = cosj * cosi * sinB
                        - cosA * cosi * sinj
                        - sinA * sini
                        + cosB * (cosA * sini - sinA * cosi * sinj);

                if (xp >= 0 && xp < width && yp >= 0 && yp < height && ooz > z[idx]) {
                    z[idx] = ooz;
                    int lum = (int)(L * 8.0f);
                    if (lum < 0) lum = 0;
                    if (lum > 11) lum = 11;
                    b[idx] = ".,-~:;=!*#$@"[lum];
                }
            }
        }

        printf("\x1b[H");
        for (int k = 0; k < width * height; k++) {
            putchar(k % width ? b[k] : '\n');
        }

        A += 0.04f;
        B += 0.02f;
        usleep(30000);
    }

    return 0;
}

Reference: Donut Math Explanation

1. Warm-Up: Typing Practice

2. Core Challenge: Spinning Donut in C

3. LeetCode Problems (in C)