LeetCode：存在重复

C++示例程序：

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        unordered_map<int, int> um;
        for (int i = 0; i < nums.size(); ++i) {
            if (um.find(nums[i]) != um.end()) return true;
            um[nums[i]];
        }
        return false;
        
    }
};