single number和变体

//XOR版本

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int length = nums.size();
        int num = 0;
        for(int i = 0;i < length;i++)
            num ^= nums[i];
        return num;
    }
};


class Solution{
public:
    int singleNumber(vector<int>& nums){
        return single_core(nums,0,nums.size()-1);
    }
    int single_core(vector<int> nums,int start,int end){
        if(start == end)
            return nums[start];
        int length = end - start + 1;
        int mid = length/2;
        if((length/2)%2 == 0){
            if(nums[i] == nums[i-1])
                return single_core(nums,start,mid);
            if(nums[i] == nums[i+1])
                return single_core(nums,mid,end);
        }
        else{
            if(nums[i] == nums[i-1])
                return single_core(nums,mid+1,end);
            if(nums[i] == nums[i+1])
                return single_core(nums,start,mid-1);
        }
    }
}