Sdmg15 - 1 year ago 117

Java Question

**i'm facing an error on my pascal triangle, but i don't know whether**

it's java or my code which is the problem. here is the code:

`import java.util.Scanner;`

public class sdz {

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

int levels;

levels = sc.nextInt();

for(int i = 0; i <= levels; i++){

for(int j =0; j <= i; j++){

System.out.print(combinatorial(i,j) + " ");

}

System.out.println();

}

}

static int fact(int n ){

if(n > 0)

return n * fact(n-1);

else

return 1;

}

static int combinatorial(int n , int r){

return fact(n)/(fact(r) * fact(n-r));

}

}

When i input the level to 13 it fails here's the result

The loop at 13

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Answer Source

I don't know if its an integer overflow or anything else. Can we write the solution with less hassle?

```
public static void pascalTriangle(int levels) {
for (int i = 0; i <= levels; i++) {
List<Integer> row = new ArrayList<>();
int s = 1;
for (int j = 0; j <= i; j++) {
row.add(s);
s = s * (i - j) / (j + 1);
}
System.out.println(row);
}
}
```

Here I've used the formula of binomial coefficient ** nCr+1 = nCr * (n -r) / (r + 1)**. I am using the already calculated result

`nCr`

to avoid repetitive calculation. In your version, you calculated factorial from scratch every time. Perhaps using memorization would be useful.

Moreover you don't actually need to do any combinatoric stuffs to calculate pascal triangle. You can simply do some addition on previous level to get current level.

```
public static void pascalTriangle(int levels) {
if (levels == 0) return;
List<Integer> currList = new ArrayList<>();
System.out.println("1");
for (int i = 2; i <= levels; i++) {
List<Integer> prevList = new ArrayList<>(currList);
currList.clear();
currList.add(1);
for (int j = 0, k = 1; k < prevList.size(); j++, k++) {
currList.add(prevList.get(j) + prevList.get(k));
}
currList.add(1);
System.out.println(currList);
}
}
```

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