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.

给你一个数组，如果有重复的数，返回true

思路1

先排序，然后第一个和第二个比较……直到结束

class Solution {
public:
bool containsDuplicate(vector<int>& nums) {

sort(nums.begin(),nums.end());
for( int i=1; i<nums.size(); i++)
{
if(nums[i-1] == nums[i])
return true;
}
return false;
}
};

思路2

直接往set中放，边放边查

类似还可以用Map hashset等等

class Solution {
public:
bool containsDuplicate(vector<int>& nums) {

set<int> set;

for(int i=0; i<nums.size(); i++)
{
if(set.find(nums[i]) != set.end())
return true;
set.insert(nums[i]);
}
return false;
}
};

最后放个大

class Solution {
public:
bool containsDuplicate(vector<int>& nums) {

return
nums.size() > set<int> (nums.begin(), nums.end()).size();

}
};