Majority Element

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Problem

Given an array nums of size n, return the majority element.

The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array.

Example 1:

Input: nums = [3,2,3]
Output: 3

Example 2:

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

Pseudocode

make a map of unique numbers and the number of occurances, return majority element immediately if > n / 2 is found

Solution

var majorityElement = function (nums) {
  const len = nums.length;
  const map = {};

  for (let i = 0; i < len; i++) {
    if (!map[nums[i]]) {
      map[nums[i]] = 0;
    }

    map[nums[i]]++;

    if (map[nums[i]] > len / 2) {
      return nums[i];
    }
  }
};

Time and Space Complexity

Time

• Loop through array once to find unique numbers and their counts - O(N)

• Total - O(N)

Space

• Storing a map of unique numbers and their counts - O(N)

• Total - O(N)