两数之和

class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer,Integer> map = new HashMap<>();
        for(int i = 0; i< nums.length; i++){
            int num  = nums[i];
            if(map.containsKey(num)){
                return new int[]{i, map.get(num)};
            }
            map.put(target-num, i);
        }
        return null;
    }
}

字母的异分词

class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        Map<String, List<String>> map = new HashMap<>();
        for(int i = 0; i< strs.length; i++){
            char[] c =  strs[i].toCharArray();
            Arrays.sort(c);
            String key = new String(c);
            List<String> list = map.getOrDefault(key, new ArrayList<>());
            list.add(strs[i]);
            map.put(key, list);
        }
        return new ArrayList<List<String>>(map.values());

    }   
}

最长连续序列

class Solution {
    public int longestConsecutive(int[] nums) {
        if(nums == null || nums.length == 0){
            return 0;
        }
        Arrays.sort(nums);
       
        Set<Integer> set = new LinkedHashSet<>();
        for (int num : nums) {
            set.add(num);
        }
        int res = 1;
        int tmp =1;
        int pre = Integer.MIN_VALUE;

        for(int num : set){
            if(num-pre == 1){
                tmp++;
            } else{
                tmp =1;
            }
            pre= num;
            res = Math.max(res, tmp);
        }  
        return res;

    }
}