mirror of
https://github.com/golang/go
synced 2024-11-13 16:50:23 -07:00
00f9f0c056
note that sortmain.go has been run through hg gofmt; only the formatting of the day initializers changed. i'm happy to revert that formatting if you'd prefer. stop on error in doc/progs/run R=r CC=golang-dev https://golang.org/cl/850041
132 lines
1.9 KiB
Go
132 lines
1.9 KiB
Go
// $G $F.go && $L $F.$A && ./$A.out
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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type Number struct {
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next *Number
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}
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// -------------------------------------
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// Peano primitives
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func zero() *Number {
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return nil
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}
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func is_zero(x *Number) bool {
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return x == nil
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}
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func add1(x *Number) *Number {
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e := new(Number)
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e.next = x
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return e
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}
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func sub1(x *Number) *Number {
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return x.next
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}
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func add(x, y *Number) *Number {
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if is_zero(y) {
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return x
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}
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return add(add1(x), sub1(y))
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}
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func mul(x, y *Number) *Number {
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if is_zero(x) || is_zero(y) {
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return zero()
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}
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return add(mul(x, sub1(y)), x)
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}
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func fact(n *Number) *Number {
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if is_zero(n) {
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return add1(zero())
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}
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return mul(fact(sub1(n)), n)
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}
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// -------------------------------------
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// Helpers to generate/count Peano integers
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func gen(n int) *Number {
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if n > 0 {
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return add1(gen(n - 1))
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}
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return zero()
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}
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func count(x *Number) int {
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if is_zero(x) {
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return 0
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}
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return count(sub1(x)) + 1
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}
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func check(x *Number, expected int) {
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var c = count(x)
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if c != expected {
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print("error: found ", c, "; expected ", expected, "\n")
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panic("fail")
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}
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}
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// -------------------------------------
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// Test basic functionality
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func verify() {
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check(zero(), 0)
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check(add1(zero()), 1)
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check(gen(10), 10)
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check(add(gen(3), zero()), 3)
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check(add(zero(), gen(4)), 4)
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check(add(gen(3), gen(4)), 7)
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check(mul(zero(), zero()), 0)
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check(mul(gen(3), zero()), 0)
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check(mul(zero(), gen(4)), 0)
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check(mul(gen(3), add1(zero())), 3)
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check(mul(add1(zero()), gen(4)), 4)
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check(mul(gen(3), gen(4)), 12)
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check(fact(zero()), 1)
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check(fact(add1(zero())), 1)
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check(fact(gen(5)), 120)
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}
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// -------------------------------------
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// Factorial
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func main() {
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verify()
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for i := 0; i <= 9; i++ {
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print(i, "! = ", count(fact(gen(i))), "\n")
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}
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}
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