kangaroo solution

    #include <assert.h>
    #include <limits.h>
    #include <math.h>
    #include <stdbool.h>
    #include <stddef.h>
    #include <stdint.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>

    char* readline();
    char** split_string(char*);

    // Complete the kangaroo function below.

    // Please either make the string static or allocate on the heap. For example,
    // static char str[] = "hello world";
    // return str;
    //
    // OR
    //
    // char* str = "hello world";
    // return str;
    //
    char* kangaroo(int x1, int v1, int x2, int v2) {

    char *yes = "YES";
    char *no = "NO";

    if(v1 == v2) return no;

    int n = (x1 - x2 + v2 - v1)/(v2 - v1);
    int m = (x1 - x2 + v2 - v1)%(v2 - v1);

    if((n>0) && (m==0))
        return yes;
    else
        return no;

    }

    int main()
    {
        FILE* fptr = fopen(getenv("OUTPUT_PATH"), "w");

        char** x1V1X2V2 = split_string(readline());

        char* x1_endptr;
        char* x1_str = x1V1X2V2[0];
        int x1 = strtol(x1_str, &x1_endptr, 10);

        if (x1_endptr == x1_str || *x1_endptr != '\0') { exit(EXIT_FAILURE); }

        char* v1_endptr;
        char* v1_str = x1V1X2V2[1];
        int v1 = strtol(v1_str, &v1_endptr, 10);

        if (v1_endptr == v1_str || *v1_endptr != '\0') { exit(EXIT_FAILURE); }

        char* x2_endptr;
        char* x2_str = x1V1X2V2[2];
        int x2 = strtol(x2_str, &x2_endptr, 10);

        if (x2_endptr == x2_str || *x2_endptr != '\0') { exit(EXIT_FAILURE); }

        char* v2_endptr;
        char* v2_str = x1V1X2V2[3];
        int v2 = strtol(v2_str, &v2_endptr, 10);

        if (v2_endptr == v2_str || *v2_endptr != '\0') { exit(EXIT_FAILURE); }

        char* result = kangaroo(x1, v1, x2, v2);

        fprintf(fptr, "%s\n", result);

        fclose(fptr);

        return 0;
    }

    char* readline() {
        size_t alloc_length = 1024;
        size_t data_length = 0;
        char* data = malloc(alloc_length);

        while (true) {
            char* cursor = data + data_length;
            char* line = fgets(cursor, alloc_length - data_length, stdin);

            if (!line) { break; }

            data_length += strlen(cursor);

            if (data_length < alloc_length - 1 || data[data_length - 1] == '\n') { break; }

            size_t new_length = alloc_length << 1;
            data = realloc(data, new_length);

            if (!data) { break; }

            alloc_length = new_length;
        }

        if (data[data_length - 1] == '\n') {
            data[data_length - 1] = '\0';
        }

        data = realloc(data, data_length);

        return data;
    }

    char** split_string(char* str) {
        char** splits = NULL;
        char* token = strtok(str, " ");

        int spaces = 0;

        while (token) {
            splits = realloc(splits, sizeof(char*) * ++spaces);
            if (!splits) {
         return splits;
            }

            splits[spaces - 1] = token;

            token = strtok(NULL, " ");
        }

        return splits;
    }