LeetCode--Contains Duplicate

题目:

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.

代码:

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

运用unordered_map,将每个数一次加入map中,如果他出现过,直接返回true,遍历完都没出现则返回false