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66 lines
1.5 KiB
Markdown
Executable File
66 lines
1.5 KiB
Markdown
Executable File
# [169. Majority Element](https://leetcode.com/problems/majority-element/)
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## 题目
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Given an array of size n, find the majority element. The majority element is the element that appears **more than** `⌊ n/2 ⌋` times.
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You may assume that the array is non-empty and the majority element always exist in the array.
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**Example 1**:
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Input: [3,2,3]
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Output: 3
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**Example 2**:
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Input: [2,2,1,1,1,2,2]
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Output: 2
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## 题目大意
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给定一个大小为 n 的数组，找到其中的众数。众数是指在数组中出现次数大于 ⌊ n/2 ⌋ 的元素。你可以假设数组是非空的，并且给定的数组总是存在众数。
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## 解题思路
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- 题目要求找出数组中出现次数大于 `⌊ n/2 ⌋` 次的数。要求空间复杂度为 O(1)。简单题。
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- 这一题利用的算法是 Boyer-Moore Majority Vote Algorithm。[https://www.zhihu.com/question/49973163/answer/235921864](https://www.zhihu.com/question/49973163/answer/235921864)
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## 代码
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```go
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package leetcode
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// 解法一 时间复杂度 O(n) 空间复杂度 O(1)
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func majorityElement(nums []int) int {
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res, count := nums[0], 0
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for i := 0; i < len(nums); i++ {
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if count == 0 {
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res, count = nums[i], 1
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} else {
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if nums[i] == res {
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count++
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} else {
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count--
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}
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}
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}
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return res
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}
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// 解法二 时间复杂度 O(n) 空间复杂度 O(n)
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func majorityElement1(nums []int) int {
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m := make(map[int]int)
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for _, v := range nums {
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m[v]++
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if m[v] > len(nums)/2 {
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return v
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}
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}
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return 0
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}
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``` |