g2001_2100.s2094_finding_3_digit_even_numbers.Solution Maven / Gradle / Ivy

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package g2001_2100.s2094_finding_3_digit_even_numbers;

// #Easy #Array #Hash_Table #Sorting #Enumeration
// #2022_05_23_Time_2_ms_(99.62%)_Space_44.9_MB_(69.58%)

import java.util.Arrays;

/**
 * 2094 - Finding 3-Digit Even Numbers\.
 *
 * Easy
 *
 * You are given an integer array `digits`, where each element is a digit. The array may contain duplicates.
 *
 * You need to find **all** the **unique** integers that follow the given requirements:
 *
 * *   The integer consists of the **concatenation** of **three** elements from `digits` in **any** arbitrary order.
 * *   The integer does not have **leading zeros**.
 * *   The integer is **even**.
 *
 * For example, if the given `digits` were `[1, 2, 3]`, integers `132` and `312` follow the requirements.
 *
 * Return _a **sorted** array of the unique integers._
 *
 * **Example 1:**
 *
 * **Input:** digits = [2,1,3,0]
 *
 * **Output:** [102,120,130,132,210,230,302,310,312,320]
 *
 * **Explanation:** All the possible integers that follow the requirements are in the output array.
 *
 * Notice that there are no **odd** integers or integers with **leading zeros**. 
 *
 * **Example 2:**
 *
 * **Input:** digits = [2,2,8,8,2]
 *
 * **Output:** [222,228,282,288,822,828,882]
 *
 * **Explanation:** The same digit can be used as many times as it appears in digits.
 *
 * In this example, the digit 8 is used twice each time in 288, 828, and 882. 
 *
 * **Example 3:**
 *
 * **Input:** digits = [3,7,5]
 *
 * **Output:** []
 *
 * **Explanation:** No **even** integers can be formed using the given digits. 
 *
 * **Constraints:**
 *
 * *   `3 <= digits.length <= 100`
 * *   `0 <= digits[i] <= 9`
**/
public class Solution {
    public int[] findEvenNumbers(int[] digits) {
        int[] idx = new int[1];
        int[] result = new int[9 * 10 * 5];
        int[] digitMap = new int[10];
        for (int digit : digits) {
            digitMap[digit]++;
        }
        dfs(result, digitMap, idx, 0);
        return Arrays.copyOfRange(result, 0, idx[0]);
    }

    private void dfs(int[] result, int[] digitMap, int[] idx, int val) {
        if (val > 99) {
            result[idx[0]++] = val;
            return;
        }
        val *= 10;
        for (int i = 0; i < 10; i++) {
            if (digitMap[i] == 0 || (val == 0 && i == 0) || (val > 99 && (i & 1) == 1)) {
                continue;
            }
            digitMap[i]--;
            val += i;
            dfs(result, digitMap, idx, val);
            val -= i;
            digitMap[i]++;
        }
    }
}