C++ 代码

class Solution {
public:
    int duplicateInArray(vector<int>& nums) {
        int n = nums.size();
        for (auto v : nums)
            if (v < 0 || v > n - 1)
                return -1;

        unordered_set<int> S;
        for (auto v : nums)
            if (S.count(v))
                return v;
            else
                S.insert(v);
        return -1;
    }
};