169. Majority Element

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

 

Constraints:

  • n == nums.length
  • 1 <= n <= 5 * 104
  • -231 <= nums[i] <= 231 - 1

 

Follow-up: Could you solve the problem in linear time and in O(1) space?

Rust Solution

struct Solution;

impl Solution {
    fn majority_element(nums: Vec<i32>) -> i32 {
        let mut count = 0;
        let mut num: Option<i32> = None;
        for x in nums {
            if let Some(y) = num {
                if x == y {
                    count += 1;
                } else {
                    count -= 1;
                    if count == 0 {
                        num = None;
                    }
                }
            } else {
                num = Some(x);
                count += 1;
            }
        }
        num.unwrap()
    }
}

#[test]
fn test() {
    let nums = vec![2, 2, 1, 1, 1, 2, 2];
    assert_eq!(Solution::majority_element(nums), 2);
    let nums = vec![3, 3, 4];
    assert_eq!(Solution::majority_element(nums), 3);
}

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