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0217_contains_duplicate.cpp
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0217_contains_duplicate.cpp
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/*
* Copyright(c) 2019 Jiau Zhang
* For more information see <https://github.com/JiauZhang/algorithms>
*
* This repo is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation
*
* It is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with THIS repo. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* https://leetcode-cn.com/problems/contains-duplicate
* 题目描述:
* 给定一个整数数组,判断是否存在重复元素
*
* 如果任何值在数组中出现至少两次,函数返回 true
* 如果数组中每个元素都不相同,则返回 false
*
* 示例 1:
* 输入: [1,2,3,1]
* 输出: true
*
* 示例 2:
* 输入: [1,2,3,4]
* 输出: false
*
* 示例 3:
* 输入: [1,1,1,3,3,4,3,2,4,2]
* 输出: true
*
* 解题思路:
* 第一种:暴力法 O(n)
* 第二种:先排序,然后检查相邻的数是否相等即可 O(nlogn)
* 第三种:哈希表,如代码所示
*/
class Solution {
public:
bool containsDuplicate(vector<int>& nums) {
unordered_map<int, int> hash;
for (int i=0; i<nums.size(); i++) {
hash[nums[i]] = i;
}
return hash.size() != nums.size();
}
};