LeetCode 540. Single Element in a Sorted Array

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1 描述

Description
Given a sorted array consisting of only integers where every element appears exactly twice except for one element which appears exactly once. Find this single element that appears only once.

Example 1

• Input: [1,1,2,3,3,4,4,8,8]
• Output: 2

Example 2

• Input: [3,3,7,7,10,11,11]
• Output: 10

Note

• Your solution should run in O(log n) time and O(1) space.

2 代码

#include <iostream>
#include <vector>
using namespace std;

//方法一
//int singleNonDuplicate(vector<int>& nums) {
//	int res = 0;
//	for (const auto& num : nums)	res ^= num;
//	return res;
//}

//方法二
int singleNonDuplicate(vector<int>& nums) {
	int res = 0;
	if (nums.size() % 2)
	{
		res = nums[nums.size() - 1];
		for (int i = 0; i < nums.size() - 1; i += 2)
		{
			if (nums[i] ^ nums[i + 1])
			{
				res = nums[i];
				break;
			}
		}
	}
	return res;
}

int main()
{
	vector<int> nums = { 1,1,2 };
	int res = singleNonDuplicate(nums);
	cout << res << endl;
	system("pause");
    return 0;
}

3 解释

方法一：逻辑门异或门，即使非单调递增数组也同样适用；
方法二：只适用于单调递增的数组；