491. Increasing Subsequences

491. Increasing Subsequences

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.

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类似combination，也可以用back tracking来做

class Solution {
    public List<List<Integer>> findSubsequences(int[] nums) {
        Set<List<Integer>> rt = new HashSet<>();
        helper(rt, nums, 0, new ArrayList<>());
        
        List<List<Integer>> r = new ArrayList<>();
        r.addAll(rt);
        return r;
    }
    
    private void helper(Set<List<Integer>> rt, int[] nums, int i, List<Integer> cur) {
        if (i == nums.length) {
            if (cur.size() > 1) rt.add(cur);
            return;
        }
        
        if (cur.isEmpty() || nums[i] >= cur.get(cur.size() - 1)) {
            List<Integer> list = new ArrayList<>(cur);
            list.add(nums[i]);
            helper(rt, nums, i + 1, list);    
        }
        
        helper(rt, nums, i + 1, cur);
    }
}