python递归和运算符问题

Question

Hi I am running below code and below is output , I am getting , can someone help me why values of k is increasing after below line as function is not changing anything related to k -

@@@@@@@@@@@@@@@@@

line of output where there is confusion- " result is: 0 and k is 0 k in if loop is 1 # result is in if loop 1

---

result is: 1 and k is 1"

@@@@@@@@@ Code - @@@@@@@@@@@@@@@

def tri_recursion(k):
     print('##')
     print("k is "+ str(k))
     lp=0
     if(k>0):
        print('If loop is' +str(lp))
        lp=lp+1
        result = k+tri_recursion(k-1)
        print('k in if loop is ' + str(k) )
        print('#')
        print("result is in if loop " + str(result))
    else:
        print('""')
        result = 0
    print('****')
    print("result is: " +str(result) + " and k is " +str(k))
    return result

print("\n\nRecursion Example Results")
abc=tri_recursion(6)
#print('K is :' + k)
print('abc is ' +str(abc))

@@@@@ output @@@@@@@@@@@

Recursion Example Results

#

k is 6 If loop is0

#

k is 5 If loop is0

#

k is 4 If loop is0

#

k is 3 If loop is0

#

k is 2 If loop is0

#

k is 1 If loop is0

#

k is 0 ""

---

result is: 0 and k is 0 k in if loop is 1 # result is in if loop 1

---

result is: 1 and k is 1 k in if loop is 2 # result is in if loop 3

---

result is: 3 and k is 2 k in if loop is 3 # result is in if loop 6

---

result is: 6 and k is 3 k in if loop is 4 # result is in if loop 10

---

result is: 10 and k is 4 k in if loop is 5 # result is in if loop 15

---

result is: 15 and k is 5 k in if loop is 6 # result is in if loop 21

---

result is: 21 and k is 6 abc is 21

Answer 1

You are changing k when you pass it into tri_recursion(k) as tri_recursion(k-1) in the recursive step.

tri_recusion(k) is basically the same as k-0 + k-1 + k-2 + ....kk . So 6 will return 6+5+4+3+2+1 = 21 with each step as 0 , 0+1, 0+1+2, ...., 0+1+2+3+4+5+6 == 0,1,3,6,10,15,21