【LeetCode】217. Contains Duplicate (2 solutions)

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.

解法一：

排序，然后比较相邻元素是否相同。时间复杂度O(nlogn)，空间复杂度O(1)

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        if(nums.size() <= 1)
            return false;
        sort(nums.begin(), nums.end());
        for(int i = 1; i < nums.size(); i ++)
        {
            if(nums[i-1] == nums[i])
                return true;
        }
        return false;
    }
};

解法二：

使用unordered_map记录已经出现的元素。时间复杂度O(n)，空间复杂度O(n)

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        if(nums.size() <= 1)
            return false;
        unordered_map<int, bool> m;
        for(int i = 0; i < nums.size(); i ++)
        {
            if(m[nums[i]] == true)
                return true;
            m[nums[i]] = true;
        }
        return false;
    }
};