LeetCode #217 - Contains Duplicate

题目描述：

Given an array of integers, find if the array contains any duplicates.

Your function should return true if any value appears at least twice in the array, and it should return false if every element is distinct.

Example 1:

Input: [1,2,3,1]
Output: true

Example 2:

Input: [1,2,3,4]
Output: false

Example 3:

Input: [1,1,1,3,3,4,3,2,4,2]
Output: true

判断数组中是否包含重复元素，直接利用哈希表解决。

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