491 Increasing Subsequences

Posted 2021-01-17 tobeabetterpig

Given an integer array, your task is to find all the different possible increasing subsequences of the given array, and the length of an increasing subsequence should be at least 2 .
Example:?
Input: [4, 6, 7, 7]
Output: [[4, 6], [4, 7], [4, 6, 7], [4, 6, 7, 7], [6, 7], [6, 7, 7], [7,7], [4,7,7]]

Note:?
1. The length of the given array will not exceed 15.
2. The range of integer in the given array is [-100,100].
3. The given array may contain duplicates, and two equal integers should also be considered as a special case of increasing sequence.






class Solution {
    public List<List<Integer>> findSubsequences(int[] nums) {
      Set<List<Integer>> set = new HashSet<>();
      
      List<Integer> tempList = new ArrayList<>();
      
      
      dfs(set, tempList, nums, 0);
      return new ArrayList<>(set); // new ArrayList<>();
        
    }
  
    private void dfs(Set<List<Integer>> set, List<Integer> tempList, int[] nums, int index){
      if(tempList.size() > 1){
        set.add(new ArrayList<>(tempList));
      }
      
      // add numbers
      for(int i = index; i < nums.length; i++){
        if(tempList.size() == 0 || tempList.get(tempList.size() - 1) <= nums[i]){
          tempList.add(nums[i]);
          dfs(set, tempList, nums, i + 1 ); // be careful , not index + 1 
          tempList.remove(tempList.size() - 1);
        }
      }
    }
}


https://www.youtube.com/watch?v=dl68syidyLM&t=242s 


注意reference 写法。。这个还不熟
画 dfs 图


https://leetcode.com/problems/increasing-subsequences/discuss/97130/Java-20-lines-backtracking-solution-using-set-beats-100.