cpair.c 9.08 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
/**
 * @file cpair.c
 * @author Ivaylo Ivanov 11777707
 * @date 08.12.2018
 *
 * @brief Main program module.
 *
 * A program that searches for the closest pair of points in a set of 2D-points
 *
 *    SYNOPSIS
 *    cpair
 *
 *    EXAMPLE
 *    $ cat 1.txt
 *    4.0 4.0
 *    -1.0 1.0
 *    1.0 -1.0
 *    -4.0 -4.0
 *    $ ./cpair < 1.txt
 *    -1.000000 1.000000
 *    1.000000 -1.000000
 *
 *
 * The program accepts an array of 2D-points as an input from stdin. The input ends at EOF.
 *
 * The program does the following:
 *  - No output if the array has one point
 *  - The points if the array has 2 points
29 30 31
 *  - Otherwise, the array is split in 2 parts based on the mean of X and sent to 2 different paralell child processes.
 *    The parent watches for the return code of the children and terminates with an error if any of the children exit
 *    with anything other than success.
32 33 34 35 36 37 38 39 40 41 42
 *
 * Algorithm description when there are more than 2 points:
 *  - P1 and P2 are the closest pairs for the first and the second part respectively.
 *  - Go through all of the pairs between the points from the first half with the second half and save the shortest one in P3.
 *  - Compare P1, P2 and P3 and return the shortest one to stdout.
 *
 **/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
43 44 45
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
46

47 48
/// Node struct for linked list
typedef struct node {
49 50 51 52 53
    /**
     * points[0] - contains the X coordinate of the point
     * points[1] - contains the Y coordinate of the point
     *
     **/
54 55 56
    float points[2];
    struct node * next;
} node_t;
57

58 59
float get_x_mean(node_t * head);
float get_distance(float x1, float x2, float y1, float y2);
60 61
node_t * find_shortest_distance(node_t * list);
int wait_for_termination(pid_t child);
62 63

int main(void) {
64 65
    char input[__UINT8_MAX__] = ""; ///< An array to save the input to
    int point_num = 0; ///< Save the number of points
66 67 68 69 70
    node_t * head = NULL;

    head = malloc(sizeof(node_t));

    node_t * current = head;
71 72 73 74 75 76 77

    while(fgets(input, __INT8_MAX__, stdin) != NULL) { ///< Read line by line
        /// Split the input by whitespace as delimiter
        char *x = strtok(input, " ");
        char *y = strtok(NULL, " ");

        if(x != NULL && y != NULL) {
78 79 80 81 82 83
            /// Convert to float and save to the list
            current -> points[0] = strtof(x, NULL);
            current -> points[1] = strtof(y, NULL);
            current -> next = malloc(sizeof(node_t));
            current = current -> next;
            point_num++; ///< Increase the list length
84
        } else {
85
            fprintf(stderr, "ERROR: Ill-formed line found\n");
86 87 88 89 90
            exit(EXIT_FAILURE);
        }
    }

    if(feof(stdin) == 0) {
91
        fprintf(stderr, "ERROR: An error interrupted the read\n");
92 93 94 95 96 97 98
        exit(EXIT_FAILURE);
    }

    if(point_num == 1)
        exit(EXIT_SUCCESS);

    if(point_num == 2) {
99 100
        printf("%f %f\n", head -> points[0], head -> points[1]);
        printf("%f %f\n", head -> next -> points[0], head -> next -> points[1]);
101 102 103
        exit(EXIT_SUCCESS);
    }

104 105
    float x_mean = get_x_mean(head);

106 107
    node_t * first_part = malloc(sizeof(node_t));
    node_t * second_part = malloc(sizeof(node_t));
108

109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124
    node_t * first_part_buff = first_part;
    node_t * second_part_buff = second_part;

    /// Separate the lists based on the mean
    current = head;
    while(current != NULL) {
        if(current -> points[0] <= x_mean) {
            first_part_buff -> points[0] = current -> points[0];
            first_part_buff -> next = malloc(sizeof(node_t));
            first_part_buff = first_part_buff -> next;
        } else {
            second_part_buff -> points[0] = current -> points[0];
            second_part_buff -> next = malloc(sizeof(node_t));
            second_part_buff = second_part_buff -> next;
        }
        current = current -> next;
125 126
    }

127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147
    /**
     *  Create the pipe file descriptors and inititalize the pipes
     *
     * fd[0] - input side of pipe
     * fd[1] - output side of pipe
     *
     **/
    int pipe_a[2], pipe_b[2];

    if(pipe(pipe_a) < 0 || pipe(pipe_b) < 0) {
        fprintf(stderr, "ERROR: Failed creating the pipe\n");
        exit(EXIT_FAILURE);
    }

    pid_t child_a, child_b; ///< Create variables for the child processes
    node_t * child_a_part = NULL;
    node_t * child_b_part = NULL;

    write(pipe_a[0], first_part, sizeof(node_t)); ///< Send the first part of the array to the child

    switch(child_a = fork()) {
148
        case -1:
149
            fprintf(stderr ,"ERROR: Couldn't fork child\n");
150 151
            exit(EXIT_FAILURE);
        case 0:
152 153 154 155 156 157 158 159 160
            if(read(pipe_a[0], child_a_part, sizeof(node_t)) < 0) {
                fprintf(stderr, "ERROR: Failed reading from pipe\n");
                exit(EXIT_FAILURE);
            }
            if(write(pipe_a[1], find_shortest_distance(child_a_part), sizeof(node_t)) < 0) {
                fprintf(stderr, "ERROR: Failed writing to pipe\n");
                exit(EXIT_FAILURE);
            }
            exit(EXIT_SUCCESS);
161 162
            break;
        default:
163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181
            write(pipe_b[0], second_part, sizeof(node_t));
            switch(child_b = fork()) {
                case -1:
                    fprintf(stderr, "ERROR: Couldn't fork child\n");
                    exit(EXIT_FAILURE);
                case 0:
                    if(read(pipe_b[0], child_b_part, sizeof(node_t)) < 0) {
                        fprintf(stderr, "ERROR: Failed reading from pipe\n");
                        exit(EXIT_FAILURE);
                    }
                    if(write(pipe_b[1], find_shortest_distance(child_b_part), sizeof(node_t)) < 0) {
                        fprintf(stderr, "ERROR: Failed writing to pipe\n");
                        exit(EXIT_FAILURE);
                    }
                    exit(EXIT_SUCCESS);
                    break;
                default:
                    break;
            }
182 183 184
            break;
    }

185 186 187 188 189
    if(wait_for_termination(child_a) != EXIT_SUCCESS)
        exit(EXIT_FAILURE);

    if(wait_for_termination(child_b) != EXIT_SUCCESS)
        exit(EXIT_FAILURE);
190

191 192 193 194 195 196 197
    /// Free the memory
    free(head);
    free(first_part);
    free(first_part_buff);
    free(second_part);
    free(second_part_buff);
    free(current);
198 199 200 201 202

    exit(EXIT_SUCCESS);
}

/**
203 204 205
 * @brief Function to calculate the mean of the X coordinates from a points list
 * @details Loops through the points list, gets the sum of X coordinates and returns the mean
 * @param head - a pointer to a list with the points
206 207 208
 * @return mean of all X coordinates
 *
 **/
209 210
float get_x_mean(node_t * head) {
    node_t * current = head;
211
    float x_sum = 0;
212 213 214
    int i = 1;

    while(current != NULL) {
215 216 217
        x_sum += current -> points[0];
        current = current -> next;
        i++;
218
    }
219

220
    return x_sum/(i - 2); ///< TODO: Fix the bug with the 2 more iterations
221 222 223 224 225 226 227 228 229 230 231 232 233 234
}

/**
 * @brief Function to calculate the distance between 2 points
 * @details The function calculates the distance between 2 points
 *          in a Cartesian coordinate system, given their coordinates
 * @param x1, y1 - pair of coordinates for the first point
 *        x2, y2 - pair of coordinates for the second point
 * @return distance between the two points
 *
 **/
float get_distance(float x1, float x2, float y1, float y2) {
    return sqrt(pow((x2 - x1), 2) + pow((y2 - y1), 2));
}
235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295

/**
 * @brief Function to find the shortest distance in a list
 * @details The function gets a list of points and finds the pair
 *          with the shortest distance between them.
 * @param list - the list with points
 * @return res - a list containing the coordinates of the two closest points
 *
 **/
node_t * find_shortest_distance(node_t * list) {
    node_t * current = list;
    node_t * next = list;

    /// Setup the result list
    node_t * res = malloc(sizeof(node_t));
    res -> next = malloc(sizeof(node_t));

    int current_shortest = 0;
    int new_shortest = 0;

    while(current != NULL) {
        next = current -> next;
        if(next != NULL) {
            new_shortest = get_distance(current -> points[0], next -> points[0], current -> points[1], next -> points[1]);

            if(new_shortest < current_shortest) {
                current_shortest = new_shortest;

                /// Save the pairs
                res -> points[0] = current -> points[0];
                res -> points[1] = current -> points[1];
                res -> next -> points[0] = next -> points[0];
                res -> next -> points[1] = next -> points[1];
            }

            current = next;
        } else
            break;
    }

    return res;
}

/**
 * @briefs Function that waits for a child to close
 * @details The function waits for a child to close.
 *          If it closes successfully, it returns the exit status only.
 *          Otherwise, it prints an error message and then returns the exit status.
 * @param child - the pid of the child process
 * @return the exist status of the child process
 *
 **/
int wait_for_termination(pid_t child) {
    int exit_stat = 0;

    if(waitpid(child, &exit_stat, 0) < 0) {
        fprintf(stderr, "ERROR: Child did not exit successfully\n");
    }

    return WEXITSTATUS(exit_stat);
}