代码随想录算法刷题训练营day29：LeetCode(491)递增子序列、LeetCode(46)全排列、LeetCode(47)全排列 II

LeetCode(491)递增子序列
题目

代码

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

class Solution {
    //先取出来再定义一个函数进行判断
    public Set<List<Integer>> tempResult=new HashSet<>();
    public List<Integer> path=new ArrayList<>();
    public List<List<Integer>> findSubsequences(int[] nums) {
        int startIndex=0;
        backtracking(nums,startIndex);
        List<List<Integer>> result=new ArrayList<>(tempResult);
        return result;
    }
    public void backtracking(int[] nums,int startIndex){
        if(isSubsequences(path)){
            List<Integer> tempPath=Arrays.asList(new Integer[path.size()]);
            Collections.copy(tempPath, path);
            tempResult.add(tempPath);//子集问题不能加return
        }
        for(int i=startIndex;i<nums.length;i++){
            path.add(nums[i]);
            backtracking(nums, i+1);
            path.remove(path.size()-1);
        }
    }
    public boolean isSubsequences(List<Integer> path){
        boolean flag=true;
        if(path.size()<2)
        {
            flag=false;
        }
        List<Integer> testPath=Arrays.asList(new Integer[path.size()]);
        Collections.copy(testPath, path);
        Collections.sort(testPath);
        for(int i=0;i<path.size();i++){
            if(testPath.get(i)!=path.get(i)){
                flag=false;
            }
        }
        return flag;
    }
}

LeetCode(46)全排列
题目

代码

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

class Solution {
    public List<List<Integer>> result=new ArrayList<>();
    public List<Integer> path=new ArrayList<>();
    public List<List<Integer>> permute(int[] nums) {
        int[] used=new int[nums.length];//记录元素是否被使用
        int startIndex=0;
        backtracking(nums,used);        
        return result;
    }
    public void backtracking(int[] nums,int[] used){
        if(path.size()==nums.length){
            List<Integer> tempPath=Arrays.asList(new Integer[path.size()]);
            Collections.copy(tempPath, path);
            result.add(tempPath);
            return;
        }
         for(int i=0;i<nums.length;i++){
            if(used[i]==1){
                continue;//1-1这个分支直接没有了，直此时就能到1-2了--重点
            }
            path.add(nums[i]);
            used[i]=1;
            backtracking(nums, used);
            path.remove(path.size()-1);
            used[i]=0;//弹出来状态也得改变
         }
        
    }
}

LeetCode(47)全排列 II
题目

代码

java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

class Solution {
    public Set<List<Integer>> tempResult=new HashSet<>();//用set集合做
    public List<Integer> path=new ArrayList<>();
    public List<List<Integer>> permuteUnique(int[] nums) {
        int[] used=new int[nums.length];
        backtracking(nums,used);
        List<List<Integer>> result=new ArrayList<>(tempResult);
        return result;
    }
    public void backtracking(int[] nums,int[] used){
        if(path.size()==nums.length){
            List<Integer> tempPath=Arrays.asList(new Integer[path.size()]);
            Collections.copy(tempPath, path);
            tempResult.add(tempPath);
            return;
        }
        for(int i=0;i<nums.length;i++){
            if(used[i]==1){
                continue;
            }
            path.add(nums[i]);
            used[i]=1;
            backtracking(nums, used);
            path.remove(path.size()-1);
            used[i]=0;
        }
    }
}