540. 有序数组中的单一元素

题目链接：https://leetcode-cn.com/problems/single-element-in-a-sorted-array/

二分法
执行用时：0 ms, 在所有 Java 提交中击败了100.00% 的用户
内存消耗：46.9 MB, 在所有 Java 提交中击败了14.20% 的用户

class Solution {
    public int singleNonDuplicate(int[] nums) {
        int left = 0, right = nums.length - 1, mid;
        while(left < right) {
            mid = left + right >> 1;
            // mid是偶数时 mid+1 = mid^1 
            // mid是奇数时 mid-1 = mid^1
            if(nums[mid] == nums[mid^1]) {
                left = mid + 1;
            } else {
                right = mid;
            }
        }
        return nums[left];
    }
}

执行用时：152 ms, 在所有 Swift 提交中击败了84.62% 的用户
内存消耗：17.1 MB, 在所有 Swift 提交中击败了7.69% 的用户

class Solution {
    func singleNonDuplicate(_ nums: [Int]) -> Int {
        guard nums.count > 1 else {
            return 1
        }
        if nums[0] != nums[1] {
            return nums[0]
        }
        var cur = 0, once = 0
        for num in nums {
            if cur == 0 {
                cur += num
                once = cur
            } else if cur - num == 0{
                cur -= num
            } else {
                once = cur
                break
            }
        }
        return once
    }
}

for循环 步长2

class Solution {
    func singleNonDuplicate(_ nums: [Int]) -> Int {
        let n = nums.count
        for i in stride(from: 0, to: n-1, by: 2) {
            if nums[i] != nums[i+1] {
                return nums[i]
            }
        }
        return nums[n-1];
    }
}