【LeetCode】217 & 219

217 - Contains Duplicate

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.

Solution 1: sort then compare the adjacent number

 1 class Solution {
 2 public:
 3     bool containsDuplicate(vector<int>& nums) {     //runtime:40ms
 4         if(nums.size()<=1)return false;
 5         sort(nums.begin(),nums.end());
 6         for(int i=1;i<nums.size();i++){
 7             if(nums[i-1]==nums[i])return true;
 8         }
 9         return false;
10     }
11 };

Solution 2: map记录已存在的int

 1 class Solution {
 2 public:
 3     bool containsDuplicate(vector<int>& nums) {     //runtime:104ms
 4         if(nums.size()<=1)return false;
 5         map<int,bool> m;
 6         for(int i=0;i<nums.size();i++){
 7             if(m[nums[i]]==true)return true;
 8             m[nums[i]]=true;
 9         }
10         return false;
11     }
12 };

219 - Contains Duplicate II

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 iand j is at most k.

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        map<int,int> m;
        for(int i=0;i<nums.size();i++){
            if(m.find(nums[i])==m.end())
                m[nums[i]]=i;
            else{
                if(i-m[nums[i]]<=k)
                    return true;
                else
                    m[nums[i]]=i;
            }
        }
        return false;
    }
};