You are provided a list of data input.txt that contains a list of Rock Paper Scissors games. Each line includes the enemy's move (A for Rock, B for Paper, and C for Scissors) and our move (X for Rock, Y for Paper, and Z for Scissors).
This game comes in two parts:
X means a loss, Y means a draw, and Z means a win.If everything follows the guidelines, each part's answer will be the total score. Submit your final answer in the form flag{Part1_Part2}, where Part1 and Part2 are the answers for each part.
For each problem, we'll follow the same template. We'll break it down into the following steps:
We'll work on each of these in turn.
For this challenge, our end goal is to get the total score across the round. Since each round is independent, we don't need to store each round's score. All we need is a running total score for each round. We can do this with a single (unsigned) integer for each round.
We'll find that it's easier to complete these parts independently when we do this challenge. There is not much comparable information other than reading the file, so we'll handle each part separately.
In this stage, we'll prepare to read the data. We'll do this the same way we do this in CalorieCounting.
// open file FILE* fp = fopen("input.txt", "r"); if (fp == NULL) exit(EXIT_FAILURE); // initialize reader variables char* line = NULL; size_t len = 0;
Note that this time, we don't need the ssize_t read variable. We know the size of the data we're reading, so we don't need to store it.
Then, we need to initialize the total score to 0.
uint32_t total_score = 0;
We'll handle this one part at a time.
Part 1
For the first part, we are told the second value is the value the opponent plays. When we compare the two values, it will be easier to convert them to integers first. We can use the offset from A or X as the value for each player (meaning every move corresponds to a 0, 1, or 2).
if statement with many checks, we can check for patterns with integers.We can do the same thing for the user score as well. Since the user's move can be seen as 1 + offset, we can add this offset to the total score.
We'll use the same logic as the previous challenge to loop through each line:
while (getline(&line, &len, fp) != -1) { ... }
In each line, we can get the self and enemy scores. We'll convert them to integers
int enemy = (int)line[0] - 'A'; int self = (int)line[2] - 'X';
We'll add 1 + offset for our move's portion of the total score.
total_score += (self + 1);
Then, we need to handle the three cases. Let's think about what these cases are. Let's make a table subtracting the enemy score from self.
| Enemy / Self | 0 | 1 | 2 |
|---|---|---|---|
| 0 | 0 [D] | 1 [W] | 2 [L] |
| 1 | -1 [L] | 0 [D] | 1 [W] |
| 2 | -2 [W] | -1 [L] | 0 [D] |
In this case, we notice the following:
1 or -2.-1 or 2.0.We can simplify this into the following checks:
int difference = self - enemy; // draw case if (difference == 0) { total_score += 3; continue; } // win case if (difference == 1 || difference == -2) { total_score += 6; continue; } // loss case if (difference == -1 || difference == 2) { total_score += 0; continue; }
As a sanity check, we should never use the code after all three checks. I put a printf("Bad\n"); statement at the end to ensure this doesn't get printed.
Once all the lines are iterated for this part, we can return the total score for that round.
Part 2
For the second part, we are told the second value is the game's outcome. X is a loss, Y is a draw, and Z is a win.
There are many ways to approach this challenge. Differentiating the win, loss, and draw cases made the most sense to me. This time, converting them into integers makes less sense because we're not comparing the two values.
We'll use the same logic as the previous challenge to loop through each line:
while (getline(&line, &len, fp) != -1) { ... }
In each line, we can get the self and enemy scores. We'll leave them as characters.
char enemy = line[0]; char self = line[2];
Since self represents the score this time, we can add the score results to the total score. The score is three times its value (since the score is 0, 1, or 2).
total_score += 3 * ((int)self - 'X');
Now, we can handle the three cases.
If the result is a loss (X), and the enemy puts A, we put C (score of 2). For B, we put A; for C, we put B.
if (self == 'X') { if (enemy == 'B' || enemy == 'C') total_score += ((int)enemy - 'A'); else if (enemy == 'A') total_score += 3; else printf("Bad 1\n"); }
We can use their score for ours if the result is a draw.
else if (self == 'Y') { // total score is what enemy put total_score += (((int)enemy - 'A') + 1); }
If the result is a win, we'll follow a similar strategy to the loss case.
else if (self == 'Z') { if (enemy == 'A' || enemy == 'B') total_score += (((int)enemy - 'A') + 2); else if (enemy == 'C') total_score += 1; else printf("Bad 2\n"); }
We should never hit the else case, but we'll put one just in case.
else { printf("Bad 3\n"); }
Once we've iterated the lines, we can return the total score.
I chose to make a function for each part. We'll define the main function to call each part's function and print the result.
int main(void) { uint32_t first = part01(); uint32_t second = part02(); // print the total score printf("flag{%d_%d}\n", first, second); return 0; }
If we run this, we'll get the following output:
$ gcc -o solve solve.c && ./solve flag{12794_14979}
The full solution is below:
#include <stdio.h> #include <stdlib.h> #include <stdint.h> uint32_t part01() { // open file FILE* fp = fopen("input.txt", "r"); if (fp == NULL) exit(EXIT_FAILURE); // initialize reader variables char* line = NULL; size_t len = 0; // read the file uint32_t total_score = 0; while (getline(&line, &len, fp) != -1) { int enemy = (int)line[0] - 'A'; int self = (int)line[2] - 'X'; total_score += (self + 1); // score for self move int difference = self - enemy; // draw case if (difference == 0) { total_score += 3; continue; } // win case if (difference == 1 || difference == -2) { total_score += 6; continue; } // loss case if (difference == -1 || difference == 2) { total_score += 0; continue; } printf("Bad\n"); } // print the total score return total_score; } uint32_t part02() { // open file FILE* fp = fopen("input.txt", "r"); if (fp == NULL) exit(EXIT_FAILURE); // initialize reader variables char* line = NULL; size_t len = 0; // read the file uint32_t total_score = 0; while (getline(&line, &len, fp) != -1) { char enemy = line[0]; char self = line[2]; total_score += 3 * ((int)self - 'X'); // score for match result if (self == 'X') { if (enemy == 'B' || enemy == 'C') total_score += ((int)enemy - 'A'); else if (enemy == 'A') total_score += 3; else printf("Bad 1\n"); } else if (self == 'Y') { // total score is what enemy put total_score += (((int)enemy - 'A') + 1); } else if (self == 'Z') { if (enemy == 'A' || enemy == 'B') total_score += (((int)enemy - 'A') + 2); else if (enemy == 'C') total_score += 1; else printf("Bad 2\n"); } else { printf("Bad 3\n"); } } return total_score; } int main(void) { uint32_t first = part01(); uint32_t second = part02(); // print the total score printf("flag{%d_%d}\n", first, second); return 0; }