491.递增子序列
题目链接：491. 非递减子序列 - 力扣（LeetCode）
思路：
class Solution {
List<List<Integer>> result = new ArrayList<>();
List<Integer> path = new ArrayList<>();
public List<List<Integer>> findSubsequences(int[] nums) {
backTracking(nums, 0);
return result;
}
public void backTracking(int[] nums, int start){
if(path.size() >= 2)
result.add(new ArrayList<>(path));
HashSet<Integer> hs = new HashSet<>();
for(int i = start; i < nums.length; i++){
if(!path.isEmpty() && path.get(path.size() -1 ) > nums[i] || hs.contains(nums[i]))
continue;
hs.add(nums[i]);
path.add(nums[i]);
backTracking(nums, i + 1);
path.remove(path.size() - 1);
}
}
}46.全排列
思路：起始位置不变，利用辅助数组，选了的元素为true
class Solution {
List<List<Integer>> result = new ArrayList<>();
LinkedList<Integer> path = new LinkedList<>();
Boolean[] used;
public List<List<Integer>> permute(int[] nums) {
if(nums.length == 0){
return result;
}
used = new Boolean[nums.length];
for(int i = 0; i < nums.length; i++) {
used[i] = false;
}
backtracking(nums);
return result;
}
public void backtracking(int[] nums){
if(path.size() == nums.length){
result.add(new ArrayList<>(path));
return;
}
for(int i = 0; i < nums.length; i++){
if(used[i]) continue;
used[i] = true;
path.add(nums[i]);
backtracking(nums);
path.removeLast();
used[i] = false;
}
}
}47.全排列 II
题目链接：47. 全排列 II - 力扣（LeetCode）
思路：
class Solution {
List<List<Integer>> result = new ArrayList<>();
List<Integer> path = new ArrayList<>();
public List<List<Integer>> permuteUnique(int[] nums) {
boolean[] used = new boolean[nums.length];
Arrays.fill(used, false);
Arrays.sort(nums);
backTrack(nums, used);
return result;
}
private void backTrack(int[] nums, boolean[] used) {
if (path.size() == nums.length) {
result.add(new ArrayList<>(path));
return;
}
for (int i = 0; i < nums.length; i++) {
if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == false) {
continue;
}
if (used[i] == false) {
used[i] = true;
path.add(nums[i]);
backTrack(nums, used);
path.remove(path.size() - 1);
used[i] = false;
}
}
}
}
