面试经典150题——Day5

一、题目

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
-109 <= nums[i] <= 109

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

题目来源：leetcode

二、题解

使用hash函数，复习unordered_map的基本用法

class Solution {
public:
    int majorityElement(vector<int>& nums) {
        unordered_map<int,int> hash;
        for(int i = 0;i < nums.size();i++){
            hash[nums[i]]++;
        }
        for(int i = 0;i < nums.size();i++){
            if(hash[nums[i]] > nums.size() / 2) return nums[i];
        }
        return 0;
    }
};