1. Contains Duplicate

　　题目链接

　　题目要求：

　　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.

 　　代码如下：

 1 class Solution {
 2 public:
 3     bool containsDuplicate(vector<int>& nums) {
 4         unordered_map<int, int> hashMap;
 5         int sz = nums.size();
 6         for(int i = 0; i < sz; i++)
 7             hashMap[nums[i]]++;
 8         
 9         unordered_map<int, int>::iterator itr = hashMap.begin();
10         for(; itr != hashMap.end(); itr++)
11         {
12             if(itr->second >= 2)
13                 return true;
14         }
15         
16         return false;
17     }
18 };

　 2. Contains Duplicate II

　　题目链接

　　题目要求：

　　Given an array of integers and an integer k, find out whether there there are two distinct indices i and j in the array such that nums[i] = nums[j] and the difference between i andj is at most k.

 1 class Solution {
 2 public:
 3     bool containsNearbyDuplicate(vector<int>& nums, int k) {
 4         unordered_map<int, int> hashMap;
 5         int sz = nums.size();
 6         for(int i = 0; i < sz; i++)
 7         {
 8             if(hashMap.find(nums[i]) != hashMap.end())
 9             {
10                 int j = hashMap[nums[i]];
11                 if(i - j <= k)
12                     return true;
13                 else
14                     hashMap[nums[i]] = i;
15             }
16             else
17             {
18                 hashMap[nums[i]] = i;
19             }
20         }
21         
22         return false;
23     }
24 };