leetcode 137. Single Number II -->hashmap

落日映苍穹つ 2022-07-19 01:24 82阅读 0赞

### 137. Single Number II ###

Question Editorial Solution

[My Submissions][]

*  Total Accepted: 91816
 *  Total Submissions: 237083
 *  Difficulty: Medium

Given an array of integers, every element appears three times except for one. Find that single one.

//用hashmap和EntrySet遍历。
    public class Solution {
        public int singleNumber(int[] nums) {
            HashMap<Integer,Integer> hm = new HashMap<Integer,Integer>();
            int length = nums.length;
            if(length==1)return nums[0];
            for(int i=0;i<length;i++){
                if(hm.containsKey(nums[i])==false) hm.put(nums[i],1);
                else {
                    int temp = hm.get(nums[i]);
                    hm.put(nums[i],temp+1);
                }
            }
            int ret=0;
            for(Map.Entry e: hm.entrySet()){
                if((Integer)e.getValue()==1){  //注意修改了此处，因为EntrySet()方法返回的为Object类型
                    ret = (Integer)e.getKey();
                    break;
                }
            }
            return ret;
        }
    }

或者

//用iterator遍历hashmap
    public class Solution {
        public int singleNumber(int[] nums) {
            HashMap<Integer,Integer> hm = new HashMap<Integer,Integer>();
            int length = nums.length;
            if(length==1)return nums[0];
            for(int i=0;i<length;i++){
                if(hm.containsKey(nums[i])==false) hm.put(nums[i],1);
                else {
                    int temp = hm.get(nums[i]);
                    hm.put(nums[i],temp+1);
                }
            }
            int ret=0;
            Iterator<Integer> itr = hm.keySet().iterator();
            while(itr.hasNext()){
                Object objkey = itr.next();
                Object objvalue = hm.get(objkey);
                if((Integer)objvalue==1)return (Integer)objkey;
            }
            return 0;
        }
    }

[My Submissions]: https://leetcode.com/problems/single-number-ii/submissions/