[LeetCode 118] Pascal's Triangle

Given a non-negative integer numRows, generate the first numRows of Pascal's triangle.

<small style="box-sizing: border-box; font-size: 11.2px;">In Pascal's triangle, each number is the sum of the two numbers directly above it.</small>

Example:

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

class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> result = new ArrayList<> ();
        if (numRows <= 0)
            return result;
        
        for (int row = 1; row <= numRows; row ++) {
            List<Integer> rowEntry = new ArrayList<> ();
            
            if (row == 1) {
                rowEntry.add (1);
                result.add (rowEntry);
                continue;
            }
            
            List<Integer> lastRow = result.get (row - 2);
            
            for (int col = 0; col < row; col ++) {
                if (col == 0 || col == row - 1) {
                    rowEntry.add (1);
                    continue;
                }
                
                
                int first = lastRow.get (col - 1);
                int second = lastRow.get (col);
                rowEntry.add (first + second);
            }
            
            result.add (rowEntry);
        }
        
        return result;
    }
}