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前言

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一、力扣491. 递增子序列

class Solution {List<List<Integer>> res = new ArrayList<>();List<Integer> path = new ArrayList<>();public List<List<Integer>> findSubsequences(int[] nums) {// Arrays.sort(nums);fun(nums, 0);return res;}public void fun(int[] nums, int start){if(path.size() >= 2){res.add(new ArrayList<>(path));}if(start == nums.length){return ;}HashSet<Integer> hs = new HashSet<>();for(int i = start; i < nums.length; i ++){if(hs.contains(nums[i])){continue;}if(path.size()>=1 && path.get(path.size()-1) > nums[i]){continue;}hs.add(nums[i]);path.add(nums[i]);fun(nums, i + 1);path.remove(path.size()-1);}}
}

二、力扣47. 全排列 II

class Solution {List<List<Integer>> res = new ArrayList<>();List<Integer> path = new ArrayList<>();boolean[] flag;public List<List<Integer>> permuteUnique(int[] nums) {flag = new boolean[nums.length];Arrays.fill(flag,false);Arrays.sort(nums);fun(nums);return res;}public void fun(int[] nums){if(path.size() == nums.length){res.add(new ArrayList<>(path));return;}for(int i = 0; i < nums.length; i ++){if(i>0 && nums[i] == nums[i-1] && !flag[i-1]){continue;}if(flag[i]==false){flag[i] = true;path.add(nums[i]);fun(nums);path.remove(path.size()-1);flag[i] = false;}}}
}

三、力扣46. 全排列

class Solution {List<List<Integer>> res = new ArrayList<>();boolean[] flag;List<Integer> path = new ArrayList<>();public List<List<Integer>> permute(int[] nums) {flag = new boolean[nums.length];Arrays.fill(flag, false);fun(nums);return res;}public void fun(int[] nums){if(nums.length == path.size()){res.add(new ArrayList<>(path));return;}for(int i = 0; i < nums.length; i ++){if(flag[i] == false){flag[i] = true;path.add(nums[i]);fun(nums);flag[i] = false;path.remove(path.size()-1);}}}
}