40. Combined sum II

Java Realization

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       class 
       
       Solution {
       
       
    
       
       public 
       
       List
       
       <
       
       List
       
       <
       
       Integer
       
       >> 
       
       combinationSum2(
       
       int[] 
       
       candidates, 
       
       int 
       
       target) {
       
       
        
       
       int 
       
       len 
       
       = 
       
       candidates.
       
       length;
       
       
        
       
       List
       
       <
       
       List
       
       <
       
       Integer
       
       >> 
       
       res 
       
       = 
       
       new 
       
       ArrayList
       
       <>();
       
       
        
       
       if (
       
       len 
       
       == 
       
       0) {
       
       
            
       
       return 
       
       res;
       
       
        }
       
       

       
       
        
       
       //  Key steps 
       
       
        
       
       Arrays.
       
       sort(
       
       candidates);
       
       

       
       
        
       
       Deque
       
       <
       
       Integer
       
       > 
       
       path 
       
       = 
       
       new 
       
       ArrayDeque
       
       <>(
       
       len);
       
       
        
       
       dfs(
       
       candidates, 
       
       len, 
       
       0, 
       
       target, 
       
       path, 
       
       res);
       
       
        
       
       return 
       
       res;
       
       
    }
       
       

       
       
    
       
       /**
       
       
     
       
       * @param candidates  Candidate array 
       
       
     
       
       * @param len  Redundant variables 
       
       
     
       
       * @param begin  From the candidate array  begin  Location search begins 
       
       
     
       
       * @param target  Means surplus , This value is equal to  target, Based on the " All figures （ Include target number ） Positive integers " This condition 
       
       
     
       
       * @param path  Path from root node to leaf node 
       
       
     
       
       * @param res
       
       
     
       
       */
       
       
    
       
       private 
       
       void 
       
       dfs(
       
       int[] 
       
       candidates, 
       
       int 
       
       len, 
       
       int 
       
       begin, 
       
       int 
       
       target, 
       
       Deque
       
       <
       
       Integer
       
       > 
       
       path, 
       
       List
       
       <
       
       List
       
       <
       
       Integer
       
       >> 
       
       res) {
       
       
        
       
       if (
       
       target 
       
       == 
       
       0) {
       
       
            
       
       res.
       
       add(
       
       new 
       
       ArrayList
       
       <>(
       
       path));
       
       
            
       
       return;
       
       
        }
       
       
        
       
       for (
       
       int 
       
       i 
       
       = 
       
       begin; 
       
       i 
       
       < 
       
       len; 
       
       i
       
       ++) {
       
       
            
       
       //  Big pruning ： subtract  candidates[i]  Less than  0, Subtract the following  candidates[i + 1]、candidates[i + 2]  It must be less than  0, So with  break
       
       
            
       
       if (
       
       target 
       
       - 
       
       candidates[
       
       i] 
       
       < 
       
       0) {
       
       
                
       
       break;
       
       
            }
       
       

       
       
            
       
       //  Pruning ： Nodes with the same value on the same layer , From  2  Start , Fewer candidates , The result must be repeated , So skip , use  continue
       
       
            
       
       if (
       
       i 
       
       > 
       
       begin 
       
       && 
       
       candidates[
       
       i] 
       
       == 
       
       candidates[
       
       i 
       
       - 
       
       1]) {
       
       
                
       
       continue;
       
       
            }
       
       

       
       
            
       
       path.
       
       addLast(
       
       candidates[
       
       i]);
       
       
            
       
       //  Debug statement  ①
       
       
            
       
       // System.out.println(" Before recursion  => " + path + ", The remaining  = " + (target - candidates[i]));
       
       

       
       
            
       
       //  Because elements cannot be reused , What recursion passes down here is  i + 1  instead of  i
       
       
            
       
       dfs(
       
       candidates, 
       
       len, 
       
       i 
       
       + 
       
       1, 
       
       target 
       
       - 
       
       candidates[
       
       i], 
       
       path, 
       
       res);
       
       

       
       
            
       
       path.
       
       removeLast();
       
       
            
       
       //  Debug statement  ②
       
       
            
       
       // System.out.println(" After recursion  => " + path + ", The remaining  = " + (target - candidates[i]));
       
       
        }
       
       
    }
       
       
}
      
      
      
      

       
       
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