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IncreasingSubsequences.java
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IncreasingSubsequences.java
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/*
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]]
*/
public class Solution {
public List<List<Integer>> findSubsequences(int[] nums) {
List<List<Integer>> res = new ArrayList<>();
helper(res, new ArrayList<Integer>(), nums, 0);
return res;
}
private void helper(List<List<Integer>> res, List<Integer> list, int[] nums, int start) {
if (list.size() > 1) {
res.add(new ArrayList<Integer>(list));
}
// we have to skip duplicates in each recursion, so we use a hash set to record what we have used in this particular recursion.
Set<Integer> used = new HashSet<>();
for (int i = start; i < nums.length; i++) {
if (used.contains(nums[i])) continue;
if (list.size() == 0 || nums[i] >= list.get(list.size() - 1)) {
list.add(nums[i]);
used.add(nums[i]);
helper(res, list, nums, i + 1);
list.remove(list.size() - 1);
}
}
}
}