0118 - Pascal's Triangle

0118 - Pascal's Triangle

Given an integer numRows, return the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:

Examples

Input: numRows = 5 Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Input: numRows = 1 Output: [[1]]

Constraints

1 <= numRows <= 30

Java Solution

class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> triangle = new ArrayList<List<Integer>>();
        triangle.add(new ArrayList<>());
        triangle.get(0).add(1);
        
        for(int row = 1; row < numRows; row++) {
            List<Integer> currentRow = new ArrayList<>();
            List<Integer> prevRow = triangle.get(row-1);
            
            currentRow.add(1);
            
            for(int j = 1; j < row; j++) {
                currentRow.add(prevRow.get(j-1) + prevRow.get(j));
            }
            
            currentRow.add(1);
            triangle.add(currentRow);
        }
        
        return triangle;
    }
}