class Solution {
public:
    /**    
     * @param nums: a vector of integers
     * @return: an integer
     */
    int findMissing(vector<int> &nums) {
        // write your code here
        int n = nums.size(), i = 0;
        while (i<n) {
            while (nums[i]!=i && nums[i]<n) swap(nums[i], nums[nums[i]]);  
            ++i;
        }
        for (int i=0; i<n; ++i)
            if (nums[i]!=i) return i;
        return n;
    }
};