# 39.数组中出现次数超过一半的数字
### 一、 题目
数组中有一个数字出现的次数超过数组长度的一半，请找出这个数字。
你可以假设数组是非空的，并且给定的数组总是存在多数元素。
示例 1:
输入: \[1, 2, 3, 2, 2, 2, 5, 4, 2] 输出: 2
限制：
1 <= 数组长度 <= 50000
注意：本题与主站 169 题相同：
来源：力扣（LeetCode）
链接：
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### 二、 题解
#### 2.1 哈希表统计法
```
func majorityElementHash(_ nums: [Int]) -> Int {
var temp: [Int : Int] = [:]
for item in nums {
if let count = temp[item] {
if count == (nums.count / 2) {
return item
}
temp[item] = count + 1
}
else {
temp[item] = 1
}
}
return nums[0]
}
```
#### 2.2 数组排序法
将数组 nums 排序，数组中点的元素 一定为众数。
```
func majorityElementArray(_ nums: [Int]) -> Int {
nums.sorted()[nums.count / 2]
}
```
#### 2.3 摩尔投票法
核心理念为 票数正负抵消 。此方法时间和空间复杂度分别为 O(N) O(1) 为本题的最佳解法。
```
func majorityElementMo(_ nums: [Int]) -> Int {
var score = 0
var x = 0
for n in nums {
if score == 0 {
x = n
}
score += (x == n ? 1 : -1)
}
return x
}
```
> [算法学习笔记(78): 摩尔投票](https://zhuanlan.zhihu.com/p/387744743)
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