• An alternative is to think of this computation as:
a * b = a + a + … + a (b 次相加）
= a + a + … + a （a 与b-1次的a相加）
= a + a*(b-1)
Recursion（递归）
• This is an instance of a recursive algorithm
– Reduce a problem to a simpler (or smaller) version of the same problem, plus some simple computations
• Recursive step（递归步骤）
– Keep reducing until reach a simple case that can besolved directly
• Base case（基线条件）
• a * b = a; if b = 1 (Base case)
• a * b = a + a * (b-1); otherwise (Recursive case)
def iterMul(a,b):
if b == 1:
return a
else:
return a + iterMul(a,b-1)
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