0-1背包问题Python：为什么返回最大值

如何解决0-1背包问题Python：为什么返回最大值

# A naive recursive implementation 
# of 0-1 Knapsack Problem 
  
# Returns the maximum value that  
# can be put in a knapsack of  
# capacity W 
def knapSack(W,wt,val,n): 
  
    # Base Case 
    if n == 0 or W == 0 : 
        return 0
  
    # If weight of the nth item is  
    # more than Knapsack of capacity W,# then this item cannot be included  
    # in the optimal solution 
    if (wt[n-1] > W): 
        return knapSack(W,n-1) 
  
    # return the maximum of two cases: 
    # (1) nth item included 
    # (2) not included 
    else: 
        return max( 
            val[n-1] + knapSack( 
                W-wt[n-1],n-1),knapSack(W,n-1)) 
  
# end of function knapSack 
  
# To test above function 
val = [60,100,120] 
wt = [10,20,30] 
W = 50
n = len(val) 
print knapSack(W,n) 

为什么我们要返回最大值？我的意思是，只要我们回去，一切都很好。另一件事只是一个递归调用，如果该元素的权重大于我们的能力，那么对吗？

return val[n-1] + knapSack( W-wt[n-1],n-1)