LeetCode | Contains Duplicate
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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.
//hashmap是一个很有用也很特殊的容器,之所以特殊是因为它引入了hash查找的概念//它的查找或contains判断等方法都非常之快,因而用来做统计很好用。//而像list或array这些容器,在用contains判断时就慢的多了。//此外,在创建hash时最好指明其长度,避免rehashpublic class Solution { public boolean containsDuplicate(int[] nums) { boolean result = false; Map<Integer, Integer> myMap = new HashMap<Integer, Integer>(nums.length); for(int i=0; i<nums.length; i++){ if(myMap.containsKey(nums[i])){ //用hashmap来维护一个已遍历探查过的集合 result = true; break; }else{ myMap.put(nums[i], 1); } } return result; }}
6月28晚,修改:
应该用HashSet来维护已便利过的元素更和逻辑一些,而且,当用hashmap来维护数组index时,可能有些问题,见Contains Duplicate ||| 的分析
//重要的是用hash查找机制,来获得常数时间的contains和add操作public class Solution { public boolean containsDuplicate(int[] nums) { boolean result = false; Set<Integer> mySet = new HashSet<Integer>(); for(int i=0; i<nums.length; i++){ if(mySet.contains(nums[i])){ //用hashset来维护已经遍历过的集合 result = true; break; }else{ mySet.add(nums[i]); } } return result; }}
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