LeetCode 热题100道-Day02

三数之和

·双指针法

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
      List<List<Integer>> result = new ArrayList<>();
      Arrays.sort(nums);
        for(int i = 0; i < nums.length ; i++){
            if(nums[i] > 0){
                return result;
            }

            if(i > 0 && nums[i] == nums[i-1]){
                continue;
            }

            int left = i+1;
            int right = nums.length - 1;
            while(right > left){
                int sum = nums[i] + nums[left] + nums[right];
                if(sum < 0) {
                    left++;
                }else if(sum > 0){
                    right--;
                }else{
                    result.add(Arrays.asList(nums[i],nums[left],nums[right]));

                    while(right > left && nums[left] == nums[left+1])
                    left++;
                    while(right > left && nums[right] == nums[right-1])
                    right--;

                    right--;
                    left--;
                }
            }
        }
        return result;

    }
}

字母异位词分组

class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
             Map<String, ArrayList<String>> map = new HashMap<>();
        for (String str : strs) {
            char[] chars = str.toCharArray();
            Arrays.sort(chars);
            String key = new String(chars);
            if (!map.containsKey(key)) {
                map.put(key, new ArrayList<>());
            }
            map.get(key).add(str);
        }
        return new ArrayList<>(map.values());
    }
}