[LeetCode] Contains Duplicate

A classic problem of hash set. The unordered_set of C++ is very suitable for this problem.

The code is as follows and it should be quite self-explanatory.

    bool containsDuplicate(vector<int>& nums) {
        unordered_set<int> st;
        for (int i = 0; i < nums.size(); i++) {
            if (st.find(nums[i]) != st.end())
                return true;
            st.insert(nums[i]);
        }
        return false;
    }