Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.

You may assume that the array is non-empty and the majority element always exist in the array.

Example 1:

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

Example 2:

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

给一个大小为n的数组，找出它的多数元素。数组非空，多数元素存在。多数元素：出现次数超过n/2的元素(超过数组长度一半)。

解法1: 用两个循环跟踪统计最多次数的元素。 T：O(n*n) S: O(1)

解法2: BST, T：O(nlogn) S: O(n)

解法3：Boyer-Moore多数投票算法 Boyer–Moore majority vote algorithm，T：O(n) S: O(1)

解法4: HashMap， T：O(n) S: O(n)

Java:

public class Solution {public int majorityElement(int[] num) {int major=num[0], count = 1;for(int i=1; i<num.length;i++){if(count==0){count++;major=num[i];}else if(major==num[i]){count++;}else count--;}return major;}
}

Java：

public class Solution {public int majorityElement(int[] nums) {int res = 0, cnt = 0;for (int num : nums) {if (cnt == 0) {res = num; ++cnt;}else if (num == res) ++cnt;else --cnt;}return res;}
}

Python: T: O(n), S: O(1)

class Solution:def majorityElement(self, nums):idx, cnt = 0, 1for i in xrange(1, len(nums)):if nums[idx] == nums[i]:cnt += 1else:cnt -= 1if cnt == 0:idx = icnt = 1return nums[idx]

C++:

class Solution {
public:int majorityElement(vector<int>& nums) {int ans = nums[0], cnt = 1;for (const auto& i : nums) {if (i == ans) {++cnt;} else {--cnt;if (cnt == 0) {ans = i;cnt = 1;}}}return ans; }
};

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转载于:https://www.cnblogs.com/lightwindy/p/8606860.html

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