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思路回溯算法

public class Solution {
       public List
   
    
     > combinationSum3(int k, int n) {        List
     
      
       > totalResult=new ArrayList
       
        
         >(); int record[]={ 0,0,0,0,0,0,0,0,0,0}; process(k, n, record, 1, 0, totalResult); return totalResult; } public void process(int k,int n,int record[],int i,int currentsum,List
         
          
           > totalResult) { if(i>9) { return; } k--; record[i]=1; if(currentsum+i==n&&k==0) { List
           
             result=new ArrayList
            
             (); for(int j=0;j<10;j++) { if(record[j]==1) { result.add(j); } } totalResult.add(result); record[i]=0; return; } currentsum+=i; if(currentsum
             
              0) { process(k, n, record, i+1, currentsum, totalResult); } record[i]=0; currentsum-=i; k++; process(k, n, record, i+1, currentsum, totalResult); return; }}
             
            
           
          
         
        
       
      
     
    
   

别人的算法

public class Solution {
       public List
   
    
     > combinationSum3(int k, int n) {        List
     
      
       > res=new ArrayList
       
        
         >(); recur(new ArrayList
         
          (),res,n,1,k); return res; } public void recur(List
          
            temp,List
           
            
             > res, int tar,int k,int count){ if(tar==0&&count==0){ res.add(temp); return; } if(count==0||tar<=0)return; for(int i=k;i<=9;i++){ temp.add(i); recur(new ArrayList
             
              (temp),res,tar-i,i+1,count-1); temp.remove(temp.size()-1); } }}
             
            
           
          
         
        
       
      
     
    
   

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