491.遞增子序列

題目鏈接：491. 非遞減子序列 - 力扣（LeetCode）

class Solution {List<List<Integer>> ans = new ArrayList<>();public List<List<Integer>> findSubsequences(int[] nums) {backtrack(nums, 0, new ArrayList<>());return ans;}private void backtrack(int[] nums, int index, List<Integer> list) {if(list.size() >= 2) {ans.add(new ArrayList<>(list));}HashSet<Integer> set = new HashSet<>();for(int i = index; i < nums.length; ++i) {if(set.contains(nums[i])) {continue;}if(list.size() >= 1 && list.getLast() > nums[i]) {continue;}else {list.add(nums[i]);set.add(nums[i]);backtrack(nums, i+1, list);list.removeLast();}}}
}

46.全排列

題目鏈接：46. 全排列 - 力扣（LeetCode）

class Solution {List<List<Integer>> ans = new ArrayList<>();public List<List<Integer>> permute(int[] nums) {backtrack(nums, new boolean[nums.length], new ArrayList<>());return ans;}private void backtrack(int[] nums,boolean[] used, List<Integer> list) {if(list.size() == nums.length) {ans.add(new ArrayList<>(list));}for(int i = 0; i < nums.length; ++i) {if(used[i]) {continue;}list.add(nums[i]);used[i] = true;backtrack(nums, used, list);list.removeLast();used[i] = false;}}
}

47.全排列 II

題目鏈接：47. 全排列 II - 力扣（LeetCode）

class Solution {List<List<Integer>> ans = new ArrayList<>();public List<List<Integer>> permuteUnique(int[] nums) {Arrays.sort(nums);backtrack(nums, new boolean[nums.length], new ArrayList<>());return ans;}private void backtrack(int[] nums, boolean[] used, List<Integer> list) {if(list.size() == nums.length) {ans.add(new ArrayList<>(list));return;    }for(int i = 0; i < nums.length; ++i) {if(used[i] || (i > 0 && !used[i-1] && nums[i] == nums[i-1])) {continue;}list.add(nums[i]);used[i] = true;backtrack(nums, used, list);used[i] = false;list.removeLast();}}
}