LeetCode //C - 1291. Sequential Digits

1291. Sequential Digits

An integer has sequential digits if and only if each digit in the number is one more than the previous digit.

Return a sorted list of all the integers in the range low, high inclusive that have sequential digits.

Example 1:

Input: low = 100, high = 300

Output: 123,234

Example 2:

Input: low = 1000, high = 13000

Output: 1234,2345,3456,4567,5678,6789,12345

Constraints:

• 10 <= low <= high <= 10^9

From: LeetCode

Link: 1291. Sequential Digits

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Solution:

Ideas:

Generate every sequential-digit number by choosing its length and starting digit, then keep those within low, high.

Code:

#include <stdlib.h>

/**
 * Note: The returned array must be malloced, assume caller calls free().
 */
int* sequentialDigits(int low, int high, int* returnSize) {
    int* result = (int*)malloc(36 * sizeof(int));
    *returnSize = 0;

    for (int length = 2; length <= 9; length++) {
        for (int start = 1; start + length - 1 <= 9; start++) {
            int number = 0;

            for (int digit = start; digit < start + length; digit++) {
                number = number * 10 + digit;
            }

            if (number >= low && number <= high) {
                result[(*returnSize)++] = number;
            }
        }
    }

    return result;
}