Increasing Subsequences Problem
Description
LeetCode Problem 491.
Given an integer array nums, return all the different possible increasing subsequences of the given array with at least two elements. You may return the answer in any order.
The given array may contain duplicates, and two equal integers should also be considered a special case of increasing sequence.
Example 1:
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Input: nums = [4,6,7,7]
Output: [[4,6],[4,6,7],[4,6,7,7],[4,7],[4,7,7],[6,7],[6,7,7],[7,7]]
Example 2:
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Input: nums = [4,4,3,2,1]
Output: [[4,4]]
Constraints:
- 1 <= nums.length <= 15
- -100 <= nums[i] <= 100
Sample C++ Code using Backtracking
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class Solution {
public:
vector<vector<int>> findSubsequences(vector<int>& nums) {
vector<vector<int>> res;
vector<int> seq;
dfs(res, seq, nums, 0);
return res;
}
void dfs(vector<vector<int>>& res, vector<int>& seq, vector<int>& nums, int pos) {
if(seq.size() > 1) res.push_back(seq);
unordered_set<int> hash;
for(int i = pos; i < nums.size(); ++i) {
if((seq.empty() || nums[i] >= seq.back()) && hash.find(nums[i]) == hash.end()) {
seq.push_back(nums[i]);
dfs(res, seq, nums, i + 1);
seq.pop_back();
hash.insert(nums[i]);
}
}
}
};