Zach S. - Solving Mars Lander

This document will walk you through solving the Mars Lander puzzle on codingame.com

The puzzle focuses on the use of conditions in the C language

Press here for a review of conditional statements in C

Thoughts Before Coding

This game has you controlling a lander to safely land it on mars. Using the lander’s speed, thrust, and angle, the user must code an algorithm to land on Mars without exploding

For the puzzle we are given seven integer type variables

1. X coordinate of the rocket

2. Y coordinate of the rocket

3. Horizontal Speed

4. Vertical Speed

5. Fuel Level

6. Angle of Rotation

7. Thrust Power

Things to consider

• How quickly will the fuel run out?

• At what elevation does speed need to be sharply reduced?

• What is the maximum speed the lander can have and still make a safe landing (Safe meaning not blowing up on impact)

1. Fuel will constantly be used as you thrust upwards. If you do not get landed fast enough, you will run out of fuel and crash into the ground

2. The elevation and speed are tightly linked. You MUST make sure the lander is not traveling to quickly when low in elevation, but also must have enough speed to reach the ground before running out of fuel

• The fuel is very limited, limited enough that if you spend to much time not on the ground, you will lose all thrust and slam into the ground

• The elevation is key for speed control. Once at a certain speed at a certain elevation, the full force thrust of the lander simply will not slow you down enough to stop from crashing into the ground

For this puzzle, all we need to worry about is the Y coordinate of the rocket, the vertical speed, the fuel level, and the thruster power.

Only paying attention to your Y coordinate, the vertical speed, the fuel level, and the thruster power is because of the level of Mars Lander. Later in the series with part two you have more variables due to the harsher landing conditions. In this level it is a completely flat landing area so not as advanced.

Implementing Code

All code below down to the next bold message is pre generated code for the game

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
 
 

Auto-generated code below aims at helping you parse the standard input according to the problem statement.

 
 
int main()
{

the number of points used to draw the surface of Mars.

    int surface_n;
    scanf("%d", &surface_n);
    for (int i = 0; i < surface_n; i++) {

X coordinate of a surface point. (0 to 6999)

        int land_x;

Y coordinate of a surface point. By linking all the points together in a sequential fashion, you form the surface of Mars.

        int land_y;
        scanf("%d%d", &land_x, &land_y);
    }
 

game loop

    while (1) {
        int X;
        int Y;

the horizontal speed (in m/s), can be negative.

        int h_speed;

the vertical speed (in m/s), can be negative.

        int v_speed;

the quantity of remaining fuel in liters.

        int fuel;

the rotation angle in degrees (-90 to 90).

        int rotate;

the thrust power (0 to 4).

        int power;
        scanf("%d%d%d%d%d%d%d", &X, &Y, &h_speed, &v_speed, &fuel, &rotate, &power);
 

The code below contains the solution, everything above was pre generated for this puzzle

The solution begins with an if else statement that looks at the Y altitude. If the lander is more than 1250 meters high, it will retain a speed of -25 m/s as to not gain too much speed and lose control.

The else statements attached to the two nested if else conditions are set to make the thruster level 1. Setting the thruster to the lowest level when we are not at our target speed helps us maintain said speed.

 
 
        if(Y > 1250)
        {
            if(v_speed < -25)
            {

You use the printf function to choose your thruster strength on a level 0-4. The first number, or the zero you see, of the function can be ignored, while the second number is your thrust power selection

                printf("0 4\n");
            }
            else
            {
                printf("0 1\n");
            }
        }

Once below 1250 meters, the else condition is set to run. This is because at this distance you need to begin slowing down as to not crash onto the ground. Though instead of -8 we could have used -1 for a guaranteed safe landing, we have to take fuel into account. -8 m/s is the slowing you can get to at our altitude of 1250 meters and still have enough fuel to make it to the ground.

        else
        {
            if(v_speed < -8)
            {
                printf("0 4\n");
            }
            else
            {
                printf("0 1\n");
            }
        }

    }

    return 0;
}
 

ATTENTION: The height of 1250m and thrust power of 4 is just one way to solve this puzzle. If you allow the max speed to be -40, the minimum height could be adjusted along with the appropriate thrust.

To summarize, this puzzle can be solved with a nearly infinite amount of methods, depending on the coders preference

Congrats! You have landed on Mars succesfully!