I have some code for Pascal's Triangle using big.Int. How do I add the values? I get an error:
invalid operation:
PascalTriangle[r - 1][c - 1] + PascalTriangle[r - 1][c]
(operator + not defined on struct)
I am using a big.Int array so I cannot use Add from the big package.
func generatePascalTriangle(n int) [][]big.Int {
PascalTriangle := make([][]big.Int, n)
for i := range PascalTriangle {
PascalTriangle[i] = make([]big.Int, n)
}
var one big.Int
one.SetInt64(1)
for r := 0; r < n; r++ {
PascalTriangle[r][0] = one
PascalTriangle[r][r] = one
}
for r := 2; r < n; r++ {
for c := 1; c < r; c++ {
PascalTriangle[r][c] = PascalTriangle[r-1][c-1] + PascalTriangle[r-1][c]
}
}
return PascalTriangle
}
I am using big.Int array so cannot use "Add" from "big" package.
That claim is false. You can, and you should.
For example,
package main
import (
"fmt"
"math/big"
)
func generatePascalTriangle(n int) [][]big.Int {
PascalTriangle := make([][]big.Int, n)
for i := range PascalTriangle {
PascalTriangle[i] = make([]big.Int, n)
}
var one big.Int
one.SetInt64(1)
for r := 0; r < n; r++ {
PascalTriangle[r][0] = one
PascalTriangle[r][r] = one
}
for r := 2; r < n; r++ {
for c := 1; c < r; c++ {
// PascalTriangle[r][c] = PascalTriangle[r-1][c-1] + PascalTriangle[r-1][c]
PascalTriangle[r][c] = *PascalTriangle[r][c].Add(&PascalTriangle[r-1][c-1], &PascalTriangle[r-1][c])
}
}
return PascalTriangle
}
func main() {
t := generatePascalTriangle(7)
for i, r := range t {
for _, n := range r[:i+1] {
fmt.Print(n.String() + " ")
}
fmt.Println()
}
}
Playground: https://play.golang.org/p/KUGsjr8Mon5
Output:
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
I am trying to create a solution for Project Euler #145. I am writing in Go. When I run my program I get a result of 125. The expected result is 120. I have 2 different ways I have tried to write the code but both come up with the same answer. Any help pointing out my error would be appreciated.
Code option #1 using strings:
package main
import (
"fmt"
"strconv"
)
//checks to see if all the digits in the number are odd
func is_Odd(sum int) bool {
intString := strconv.Itoa(sum)
for x := len(intString); x > 0; x-- {
newString := intString[x-1]
if newString%2 == 0 {
return false
}
}
return true
}
//reverse the number passed
func reverse_int(value int) int {
intString := strconv.Itoa(value)
newString := ""
for x := len(intString); x > 0; x-- {
newString += string(intString[x-1])
}
newInt, err := strconv.Atoi(newString)
if err != nil {
fmt.Println("Error converting string to int")
}
return newInt
}
//adds 2 int's passed to it and returns an int
func add(x int, y int) int {
return x + y
}
func main() {
//functions test code
/*y := 35
x := reverse_int(y)
z := add(x,y)
fmt.Println(is_Odd(z))*/
counter := 1
for i := 1; i < 1000; i++ {
flipped := reverse_int(i)
sum := add(flipped, i)
oddCheck := is_Odd(sum)
if oddCheck {
fmt.Println(counter, ":", i, "+", flipped, "=", sum)
counter++
}
}
counter--
fmt.Println("total = ", counter)
}
Code option #2 using only ints:
package main
import (
"fmt"
)
var counter int
//breaks down an int number by number and checks to see if
//all the numbers in the int are odd
func is_Odd(n int) bool {
for n > 0 {
remainder := n % 10
if remainder%2 == 0 {
return false
}
n /= 10
}
return true
}
//adds 2 int's passed to it and returns an int
func add(x int, y int) int {
return x + y
}
//reverses the int passed to it and returns an int
func reverse_int(n int) int {
var new_int int
for n > 0 {
remainder := n % 10
new_int *= 10
new_int += remainder
n /= 10
}
return new_int
}
func main() {
//functions test code
/*y := 35
x := reverse_int(y)
z := add(x,y)
fmt.Println(is_Odd(z))*/
counter = 1
for i := 1; i < 1000; i++ {
flipped := reverse_int(i)
sum := add(flipped, i)
oddCheck := is_Odd(sum)
if oddCheck {
//fmt.Println(counter,":",i,"+",flipped,"=",sum)
counter++
}
}
counter--
fmt.Println(counter)
}
Leading zeroes are not allowed in either n or reverse(n) so in reverse(n int) int remove Leading zeroes like so:
remainder := n % 10
if first {
if remainder == 0 {
return 0
}
first = false
}
try this:
package main
import (
"fmt"
)
//breaks down an int number by number and checks to see if
//all the numbers in the int are odd
func isOdd(n int) bool {
if n <= 0 {
return false
}
for n > 0 {
remainder := n % 10
if remainder%2 == 0 {
return false
}
n /= 10
}
return true
}
//adds 2 int's passed to it and returns an int
func add(x int, y int) int {
return x + y
}
//reverses the int passed to it and returns an int
func reverse(n int) int {
first := true
t := 0
for n > 0 {
remainder := n % 10
if first {
if remainder == 0 {
return 0
}
first = false
}
t *= 10
t += remainder
n /= 10
}
return t
}
func main() {
counter := 0
for i := 0; i < 1000; i++ {
flipped := reverse(i)
if flipped == 0 {
continue
}
sum := add(flipped, i)
if isOdd(sum) {
counter++
//fmt.Println(counter, ":", i, "+", flipped, "=", sum)
}
}
fmt.Println(counter)
}
output:
120
You're ignoring this part of the criteria:
Leading zeroes are not allowed in either n or reverse(n).
Five of the numbers you count as reversible end in 0. (That means their reverse has a leading zero.) Stop counting those as reversible and you're done.
Some positive integers n have the property that the sum [ n +
reverse(n) ] consists entirely of odd (decimal) digits. For instance,
36 + 63 = 99 and 409 + 904 = 1313. We will call such numbers
reversible; so 36, 63, 409, and 904 are reversible. Leading zeroes are
not allowed in either n or reverse(n).
All digits of the sum must all be odd.
Try this one: https://play.golang.org/p/aUlvKrb9SB
I'm trying to create a program capable to generate combinations from a given range.
I started editing this code below that generates combinations:
package main
import "fmt"
func nextPassword(n int, c string) func() string {
r := []rune(c)
p := make([]rune, n)
x := make([]int, len(p))
return func() string {
p := p[:len(x)]
for i, xi := range x {
p[i] = r[xi]
}
for i := len(x) - 1; i >= 0; i-- {
x[i]++
if x[i] < len(r) {
break
}
x[i] = 0
if i <= 0 {
x = x[0:0]
break
}
}
return string(p)
}
}
func main() {
np := nextPassword(2, "ABCDE")
for {
pwd := np()
if len(pwd) == 0 {
break
}
fmt.Println(pwd)
}
}
This is the Output of the code:
AA
AB
AC
AD
AE
BA
BB
BC
BD
BE
CA
CB
CC
CD
CE
DA
DB
DC
DD
DE
EA
EB
EC
ED
EE
And this is the code I edited:
package main
import "fmt"
const (
Min = 5
Max = 10
)
func nextPassword(n int, c string) func() string {
r := []rune(c)
p := make([]rune, n)
x := make([]int, len(p))
return func() string {
p := p[:len(x)]
for i, xi := range x {
p[i] = r[xi]
}
for i := len(x) - 1; i >= 0; i-- {
x[i]++
if x[i] < len(r) {
break
}
x[i] = 0
if i <= 0 {
x = x[0:0]
break
}
}
return string(p)
}
}
func main() {
cont := 0
np := nextPassword(2, "ABCDE")
for {
pwd := np()
if len(pwd) == 0 {
break
}
if cont >= Min && cont <= Max{
fmt.Println(pwd)
} else if cont > Max{
break
}
cont += 1
}
}
Output:
BA
BB
BC
BD
BE
CA
My code works, but if I increase the length of the combination and my range starts from the middle, the program will generate even the combinations that I don't want (and of course that will take a lot of time).
How can I solve this problem?
I really didn't like how nextPassword was written, so I made a variation. Rather than starting at 0 and repeatedly returning the next value, this one takes an integer and converts it to the corresponding "password." E.g. toPassword(0, 2, []rune("ABCDE")) is AA, and toPassword(5, ...) is BA.
From there, it's easy to loop over whatever range you want. But I also wrote a nextPassword wrapper around it that behaves similarly to the one in the original code. This one uses toPassword under the cover and takes a starting n.
Runnable version here: https://play.golang.org/p/fBo6mx4Mji
Code below:
package main
import (
"fmt"
)
func toPassword(n, length int, alphabet []rune) string {
base := len(alphabet)
// This will be our output
result := make([]rune, length)
// Start filling from the right
i := length - 1
// This is essentially a conversion to base-b, where b is
// the number of possible letters (5 in the case of "ABCDE")
for n > 0 {
// Filling from the right, put the right digit mod b
result[i] = alphabet[n%base]
// Divide the number by the base so we're ready for
// the next digit
n /= base
// Move to the left
i -= 1
}
// Fill anything that's left with "zeros" (first letter of
// the alphabet)
for i >= 0 {
result[i] = alphabet[0]
i -= 1
}
return string(result)
}
// Convenience function that just returns successive values from
// toPassword starting at start
func nextPassword(start, length int, alphabet []rune) func() string {
n := start
return func() string {
result := toPassword(n, length, alphabet)
n += 1
return result
}
}
func main() {
for i := 5; i < 11; i++ {
fmt.Println(toPassword(i, 2, []rune("ABCDE")))
} // BA, BB, BC, BD, BE, CA
// Now do the same thing using nextPassword
np := nextPassword(5, 2, []rune("ABCDE"))
for i := 0; i < 6; i++ {
fmt.Println(np())
} // BA, BB, BC, BD, BE, CA
}
I am new to Go but not to programming. I am trying to implement a few functions on prime numbers as a way to learn. Here's my code, which you can run at http://ideone.com/qxLQ0D:
// prime numbers
package main
import (
"fmt"
)
// list of primes less than n:
// sieve of eratosthenes
func primes(n int) (ps []int) {
sieve := make([]bool, n)
for i := 2; i < n; i++ {
if !(sieve[i]) {
ps = append(ps, i)
for j := i * i; j < n; j += i {
sieve[j] = true
}
}
}
return ps
}
// true if n is prime, else false:
// trial division via 2,3,5-wheel
func isPrime(n int) (bool) {
wheel := [11]int{1,2,2,4,2,4,2,4,6,2,6}
w := 0
f := 2
for f*f <= n {
if n % f == 0 { return false }
f += wheel[w]
w += 1
if w == 11 { w = 3 }
}
return true
}
// greatest common divisor of x and y:
// via euclid's algorithm
func gcd(x int, y int) (int) {
for y != 0 {
x, y = y, x % y
}
return x
}
// absolute value of x
func abs(x int) (int) {
if x < 0 {
return -1 * x
}
return x
}
// list of prime factors of n:
// trial division via 2,3,5-wheel
// to 1000 followed by pollard rho
func factors(n int) (fs []int) {
wheel := [11]int{1,2,2,4,2,4,2,4,6,2,6}
w := 0 // wheel pointer
f := 2 // current trial factor
for f*f <= n && f < 1000 {
for n % f == 0 {
fs = append(fs, f)
n /= f
}
f += wheel[w]; w += 1
if w == 11 { w = 3 }
}
if n == 1 { return fs }
h := 1 // hare
t := 1 // turtle
g := 1 // greatest common divisor
c := 1 // random number parameter
for !(isPrime(n)) {
for g == 1 {
h = (h*h+c) % n // the hare runs
h = (h*h+c) % n // twice as fast
t = (t*t+c) % n // as the tortoise
g = gcd(abs(t-h), n)
}
if isPrime(g) {
for n % g == 0 {
fs = append(fs, g)
n /= g
}
}
h, t, g, c = 1, 1, 1, c+1
}
fs = append(fs, n)
return fs
}
func main() {
fmt.Println(primes(100))
fmt.Println(isPrime(997))
fmt.Println(isPrime(13290059))
fmt.Println(factors(13290059))
}
That works fine. I would like to know how to initialize wheel as a constant at compile time so that it can be shared by isPrime and factors, and I would appreciate any comments on style or other aspects of my program.
I eventually want to implement some factoring algorithms on big integers, using the math/big package. But I'm having much trouble. Simplifying to just the trial division via a 2,3,5-wheel part of the algorithm, here's my code:
package main
import (
"fmt"
"math/big"
)
func factors(n big.Int) (fs []big.Int) {
zero := big.NewInt(0);
one := big.NewInt(1);
two := big.NewInt(2);
four := big.NewInt(4);
six := big.NewInt(6);
wheel := [11]big.Int{*one,*two,*two,*four,*two,*four,*two,*four,*six,*two,*six}
w := 0;
f := two;
for big.Mul(*f, *f).Cmp(n) <= 0 {
for big.Mod(n, *f).Cmp(*zero) {
fs = append(fs, *f)
n = big.Div(n, *f)
}
f = big.Add(f, wheel[w])
w += 1
if w > 11 { w = 3 }
}
fs = append(fs, n)
return fs
}
func main() {
fmt.Println(factors(*big.NewInt(13290059)))
}
That doesn't work; ideone complains that the Add, Div, Mod and Mul functions are not found. And it looks rather ugly to me, stylistically.
Please tell me how to fix my factors function.
EDIT 1: Thanks to #TClaverie, I now have a function that compiles. Now I am getting a runtime error, and ideone points to the Mul function. Once again, can anyone help? My revised code is shown below and at http://ideone.com/aVBgJg:
package main
import (
"fmt"
"math/big"
)
func factors(n *big.Int) (fs []big.Int) {
var z *big.Int
zero := big.NewInt(0)
one := big.NewInt(1)
two := big.NewInt(2)
four := big.NewInt(4)
six := big.NewInt(6)
wheel := [11]*big.Int{one,two,two,four,two,four,two,four,six,two,six}
w := 0
f := two
z.Mul(f, f)
for z.Cmp(n) <= 0 {
z.Mod(n, f)
for z.Cmp(zero) == 0 {
fs = append(fs, *f)
n.Div(n, f)
z.Mod(n, f)
}
f.Add(f, wheel[w])
w += 1
if w > 11 { w = 3 }
z.Mul(f, f)
}
fs = append(fs, *n)
return fs
}
func main() {
fmt.Println(factors(big.NewInt(13290059)))
}
EDIT 2: Thanks to #TClaverie, I've learned a lot about Go, and I'm close to a solution. But I still have one problem; the program
package main
import (
"fmt"
"math/big"
)
func main() {
one := big.NewInt(1);
two := big.NewInt(2);
four := big.NewInt(4);
six := big.NewInt(6);
wheel := [11]*big.Int{one,two,two,four,two,four,two,four,six,two,six}
f := two; w := 0
for f.Cmp(big.NewInt(40)) < 0 {
fmt.Println(f, w, wheel)
f.Add(f, wheel[w])
w += 1; if w == 11 { w = 3 }
}
}
prints the following output, which shows that wheel is being modified in the call to Add:
2 0 [1 2 2 4 2 4 2 4 6 2 6]
3 1 [1 3 3 4 3 4 3 4 6 3 6]
6 2 [1 6 6 4 6 4 6 4 6 6 6]
12 3 [1 12 12 4 12 4 12 4 6 12 6]
16 4 [1 16 16 4 16 4 16 4 6 16 6]
32 5 [1 32 32 4 32 4 32 4 6 32 6]
36 6 [1 36 36 4 36 4 36 4 6 36 6]
What's the right way to prevent that from happening?
So, if you look at the documentation, you'll see that Add, Div and Mul are defined for the type *big.Int, so you have to call them using a *big.Int with the dot notation. Also, they expect arguments of type *big.Int, but you're giving them big.Int.
If you look at the documentation, you'll also see that those functions are of the type: z.Op(x, y). They apply x Op y and store the result into another *big.Int called z. So, you need a dummy *big.Int, that I'll call z (the methods return it at the same time).
Finally, it's better to work with pointers in this case, as all methods work with pointers.
func factors(n big.Int) (fs []big.Int) --> func factors(n *big.Int) (fs []big.Int)
wheel := [11]big.Int{*one,*two,*two,*four,*two,*four,*two,*four,*six,*two,*six} -->
wheel := [11]*big.Int{one,two,two,four,two,four,two,four,six,two,six}
big.Mul(*f, *f) --> z.Mul(f, f)
big.Mod(n, *f) --> z.Mod(n, f)
n = big.Div(n, *f) --> n.Div(n, f)
f = big.Add(f, wheel[w]) -−> f.Add(f, wheel[w])
A last thing: your condition is broken in the second for, because you are giving it an int instead of a boolean.
So, I do not guarantee the code works after those modifications, but you will be able to make it compile and debug it.
I'm writing a function that returns a sequence of numbers of variable length:
func fib(n int) ??? {
retval := ???
a, b := 0, 1
for ; n > 0; n-- {
??? // append a onto retval here
c := a + b
a = b
b = c
}
}
It can be observed that the final length of the returned sequence will be n. How and what should fib return to achieve idiomatic Go? If the length was not known in advance, how would the return value, and usage differ? How do I insert values into retval?
Here, we know how many numbers; we want n Fibonacci numbers.
package main
import "fmt"
func fib(n int) (f []int) {
if n < 0 {
n = 0
}
f = make([]int, n)
a, b := 0, 1
for i := 0; i < len(f); i++ {
f[i] = a
a, b = b, a+b
}
return
}
func main() {
f := fib(7)
fmt.Println(len(f), f)
}
Output: 7 [0 1 1 2 3 5 8]
Here, we don't know how many numbers; we want all the Fibonacci numbers less than or equal to n.
package main
import "fmt"
func fibMax(n int) (f []int) {
a, b := 0, 1
for a <= n {
f = append(f, a)
a, b = b, a+b
}
return
}
func main() {
f := fibMax(42)
fmt.Println(len(f), f)
}
Output: 10 [0 1 1 2 3 5 8 13 21 34]
You could also use IntVector from the Go vector package. Note that type IntVector []int.
Don't use Vectors, use slices. Here are some mapping of various vector operations to idiomatic slice operations.