ManasaAndFactorials.c

#include <assert.h>
#include <ctype.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* ltrim(char*);
char* rtrim(char*);

int parse_int(char*);
long parse_long(char*);

/*
 * Complete the 'solve' function below.
 *
 * The function is expected to return a LONG_INTEGER.
 * The function accepts LONG_INTEGER n as parameter.
 */
typedef long long ll;
ll countingTrailingZeros(ll m)                        
{
    if(m == 0)
    {
        return 0;
    }
    return m/5 + countingTrailingZeros(m/5);
}

// the idea is simple to binary search b/w range 0 to 5*n to find the minimum m which has n trailing zeros.

ll solve(long n)
{
    ll res = -1;
    ll l = 0;
    ll u = 5*n;

    while(l <= u)
    {
        ll mid = (l + u)/2;
        if(countingTrailingZeros(mid) >= n)
        {
            res = mid;
            u = mid - 1;
        }
        else
        {
            l = mid + 1;
        }
    }
    return res;
}

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

    int t = parse_int(ltrim(rtrim(readline())));

    for (int t_itr = 0; t_itr < t; t_itr++) {
        long n = parse_long(ltrim(rtrim(readline())));

        long result = solve(n);

        fprintf(fptr, "%ld\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;
        }

        alloc_length <<= 1;

        data = realloc(data, alloc_length);

        if (!data) {
            data = '\0';

            break;
        }
    }

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

        data = realloc(data, data_length);

        if (!data) {
            data = '\0';
        }
    } else {
        data = realloc(data, data_length + 1);

        if (!data) {
            data = '\0';
        } else {
            data[data_length] = '\0';
        }
    }

    return data;
}

char* ltrim(char* str) {
    if (!str) {
        return '\0';
    }

    if (!*str) {
        return str;
    }

    while (*str != '\0' && isspace(*str)) {
        str++;
    }

    return str;
}

char* rtrim(char* str) {
    if (!str) {
        return '\0';
    }

    if (!*str) {
        return str;
    }

    char* end = str + strlen(str) - 1;

    while (end >= str && isspace(*end)) {
        end--;
    }

    *(end + 1) = '\0';

    return str;
}

int parse_int(char* str) {
    char* endptr;
    int value = strtol(str, &endptr, 10);

    if (endptr == str || *endptr != '\0') {
        exit(EXIT_FAILURE);
    }

    return value;
}

long parse_long(char* str) {
    char* endptr;
    long value = strtol(str, &endptr, 10);

    if (endptr == str || *endptr != '\0') {
        exit(EXIT_FAILURE);
    }

    return value;
}