Function Run Fun
nefu16
We all love recursion! Don't we? Consider a three-parameter recursive
function w(a, b, c):
if a <= 0 or b <= 0 or c <= 0, then w(a, b, c) returns: 1
if a > 20 or b > 20 or c > 20, then w(a, b, c)
returns: w(20, 20, 20)
if a < b and b < c, then w(a, b, c)
returns: w(a, b, c-1) + w(a, b-1, c-1) - w(a, b-1, c)
otherwise it
returns: w(a-1, b, c) + w(a-1, b-1, c) + w(a-1, b, c-1) - w(a-1, b-1, c-1) This
is an easy function to implement. The problem is, if implemented directly, for
moderate values of a, b and c (for example, a = 15, b = 15, c = 15), the
program takes hours to run because of the massive recursion.
2021/11/3 4
第4页，共33页。
