LeetCode 136. Single Number

Given an array of integers, every elements appears twice expect for one. Find the single one. Do it without using extra memory.

This problem can be solved using "set" or Hash Map. However, it is going to use extra memory space.

// we need to consider using bit manipulation. A ^ A = 0, 0 ^ A  = A

// Since in this array, every elements appears twice expect for one. We can use above equations. 
int onlyOne(vector<int> input) {
    // we need to first check the size of input.
    if(input.size() == 0) return 0;
    int result = 0;
    for(auto it : input) {
         result ^= it;
    }
    return result;
}