Writing Pascal's Triangle using big.Int int

Question

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
}

score 1 · Answer 1 · answered Sep 18 '18 at 11:59

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

PascalTriangle[r][c] = *PascalTriangle[r][c].Add(&PascalTriangle[r-1][c-1], &PascalTriangle[r-1][c]) Basically you are assigning the pointer "*PascalTriangle[r][c]" and using addresses at particular cell to add the values in those cells. I don't know how does this work — NewToGo, Sep 18 '18 at 12:29

Writing Pascal's Triangle using big.Int int

1 Answers1