LeetCode Problem 442
Link of the Problem to try -: Link
Given an integer array nums of length n where all the integers of nums are in the range [1, n] and each integer appears at most twice, return an array of all the integers that appears twice.
You must write an algorithm that runs in O(n) time and uses only constant auxiliary space, excluding the space needed to store the output
Example 1:
Input: nums = [4,3,2,7,8,2,3,1]
Output: [2,3]
Example 2:
Input: nums = [1,1,2]
Output: [1]
Example 3:
Input: nums = [1]
Output: []
Constraints:
n == nums.length1 <= n <= 1051 <= nums[i] <= n- Each element in
numsappears once or twice.
Solution:
In this question we can use HashMap as there is we need to return that element whose frequency is equal to exactly 2 and that's why it is a very easy question that we can solve by HashMap.
Code:
HashMap<Integer, Integer> mp = new HashMap<>();
for (int i = 0; i < nums.length; i++) {
mp.put(nums[i], mp.getOrDefault(nums[i], 0) + 1);
}
List<Integer> lis = new ArrayList<>();
for (int a : mp.keySet()) {
if (mp.get(a) == 2) {
lis.add(a);
}
}
return lis;
