solved "Single Number" I and II on LeetCode (XOR!) http://oj.leetcode.com/problems/single-number/ *and* http://oj.leetcode.com/problems/single-number-ii/

single_number.cpp

class Solution {
public:
    // single number i
    int singleNumber(int A[], int n) {
        int result = 0;
        for (int i; i<n ;++i)
            result = (result ^ A[i]);
        return result;
    }

    // single number ii, like base 3 xor
    int singleNumber(int A[], int n) {
        int bitSize = CHAR_BIT * sizeof(int);
        char *bits = new char[bitSize];
        for (int i=0; i<bitSize; ++i) bits[i] = 0;
        for (int i=0; i<n; ++i) {
            for (int j=0; j<bitSize; ++j)
                bits[j] = (bits[j] + ( (A[i] >> j) & 1 )) % 3;
        }
        
        int result = 0;
        for (int i=0; i<bitSize; ++i) {
            result |= ( ((int)(bits[i] != 0)) << i );
        }
        delete[] bits;
        return result;
    }
};