[LeetCode] Contains Duplicate

KiraYin--

于 2015-06-11 13:48:11 发布

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分类专栏：易文章标签： leetcode

本文链接：https://blog.youkuaiyun.com/jellyYin/article/details/46456671

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本文介绍两种方法来检查整数数组中是否存在重复项：一种是通过排序后比较相邻元素；另一种则是使用unordered_set进行快速判断。同时提供了一个高阶数学解决方案，并对比了map、hash_map、unordered_map与unordered_set的区别。

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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.

1. Sort the array and then compare

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

2. Use unordered_set with Time complexity O(n) and space complexity O(n)

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        unordered_set<int> aset;
        for(auto i : nums)
        {
            if(aset.find(i)!=aset.end())
                return true;
            aset.insert(i);
        }
        return false;
    }
};

Another highly mathematical solution:

http://bookshadow.com/weblog/2015/06/03/leetcode-contains-duplicate-iii/

The difference between map, hash_map, unordered_map and unordered_set:

http://blog.youkuaiyun.com/u013195320/article/details/23046305