LeetCode-in-Java

3785. Minimum Swaps to Avoid Forbidden Values

Hard

You are given two integer arrays, nums and forbidden, each of length n.

You may perform the following operation any number of times (including zero):

Choose two distinct indices i and j, and swap nums[i] with nums[j].

Return the minimum number of swaps required such that, for every index i, the value of nums[i] is not equal to forbidden[i]. If no amount of swaps can ensure that every index avoids its forbidden value, return -1.

Example 1:

Input: nums = [1,2,3], forbidden = [3,2,1]

Output: 1

Explanation:

One optimal set of swaps:

Select indices i = 0 and j = 1 in nums and swap them, resulting in nums = [2, 1, 3].
After this swap, for every index i, nums[i] is not equal to forbidden[i].

Example 2:

Input: nums = [4,6,6,5], forbidden = [4,6,5,5]

Output: 2

Explanation:

One optimal set of swaps:

Select indices i = 0 and j = 2 in nums and swap them, resulting in nums = [6, 6, 4, 5].
Select indices i = 1 and j = 3 in nums and swap them, resulting in nums = [6, 5, 4, 6].
After these swaps, for every index i, nums[i] is not equal to forbidden[i].

Example 3:

Input: nums = [7,7], forbidden = [8,7]

Output: -1

Explanation:

It is not possible to make nums[i] different from forbidden[i] for all indices.

Example 4:

Input: nums = [1,2], forbidden = [2,1]

Output: 0

Explanation:

No swaps are required because nums[i] is already different from forbidden[i] for all indices, so the answer is 0.

Constraints:

1 <= n == nums.length == forbidden.length <= 10⁵
1 <= nums[i], forbidden[i] <= 10⁹

Solution

import java.util.HashMap;
import java.util.Map;

public class Solution {
    public int minSwaps(int[] nums, int[] forbidden) {
        int n = nums.length;
        Map<Integer, Integer> map = new HashMap<>();
        for (int num : nums) {
            map.put(num, map.getOrDefault(num, 0) + 1);
        }
        for (int num : forbidden) {
            map.put(num, map.getOrDefault(num, 0) + 1);
        }
        for (int val : map.values()) {
            if (val > n) {
                return -1;
            }
        }
        Map<Integer, Integer> map2 = new HashMap<>();
        int total = 0;
        for (int i = 0; i < n; i++) {
            if (nums[i] == forbidden[i]) {
                map2.put(nums[i], map2.getOrDefault(nums[i], 0) + 1);
                total++;
            }
        }
        if (total == 0) {
            return 0;
        }
        int maxSwaps = 0;
        for (int num : map2.values()) {
            maxSwaps = Math.max(maxSwaps, num);
        }
        return Math.max(maxSwaps, (total + 1) / 2);
    }
}

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