3270. Find the Key of the Numbers

Method 1

You are given three positive integers num1, num2, and num3.
The key of num1, num2, and num3 is defined as a four-digit number such that:
- Initially, if any number has less than four digits, it is padded with leading zeros.
- The ith digit (1 <= i <= 4) of the key is generated by taking the smallest digit among the ith digits of num1, num2, and num3.
Return the key of the three numbers without leading zeros (if any).

Example 1

Input: num1 = 1, num2 = 10, num3 = 1000

Output: 0

Explanation:

On padding, num1 becomes "0001", num2 becomes "0010", and num3 remains "1000".

The 1st digit of the key is min(0, 0, 1).
The 2nd digit of the key is min(0, 0, 0).
The 3rd digit of the key is min(0, 1, 0).
The 4th digit of the key is min(1, 0, 0).
Hence, the key is "0000", i.e. 0.

Example 2

Input: num1 = 987, num2 = 879, num3 = 798

Output: 777

Example 3

Input: num1 = 1, num2 = 2, num3 = 3

Output: 1

Method 1

【O(1) time | O(1) space】

package Leetcode.Math;

/**
 * @author zhengxingxing
 * @date 2025/01/11
 */
public class FindTheKeyOfTheNumbers {
    public static int findKey(int num1, int num2, int num3) {
        // Convert numbers to 4-digit strings with leading zeros
        String s1 = String.format("%04d", num1);
        String s2 = String.format("%04d", num2);
        String s3 = String.format("%04d", num3);

        StringBuilder key = new StringBuilder();

        // Iterate through each digit and find the minimum value
        for (int i = 0; i < 4; i++) {
            int digit = Math.min(Math.min(
                            s1.charAt(i) - '0',
                            s2.charAt(i) - '0'),
                    s3.charAt(i) - '0'
            );
            key.append(digit);
        }

        // Convert to integer and return
        return Integer.parseInt(key.toString());
    }

    public static void main(String[] args) {
        // Test case 1
        System.out.println("Test case 1:");
        int num1 = 1, num2 = 10, num3 = 1000;
        System.out.println("Input: num1 = " + num1 + ", num2 = " + num2 + ", num3 = " + num3);
        System.out.println("Output: " + findKey(num1, num2, num3));

        // Test case 2
        System.out.println("\nTest case 2:");
        num1 = 987; num2 = 879; num3 = 798;
        System.out.println("Input: num1 = " + num1 + ", num2 = " + num2 + ", num3 = " + num3);
        System.out.println("Output: " + findKey(num1, num2, num3));

        // Test case 3
        System.out.println("\nTest case 3:");
        num1 = 1; num2 = 2; num3 = 3;
        System.out.println("Input: num1 = " + num1 + ", num2 = " + num2 + ", num3 = " + num3);
        System.out.println("Output: " + findKey(num1, num2, num3));
    }
}

Method 1

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