118-pascal's-triangle.java

/**
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:

Example 1:

Input: numRows = 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<>();
        
        for(int i = 0 ; i < numRows; i++) {
            List<Integer> list = new ArrayList<>();
            
            for(int j = 0; j < i + 1 ; j++) {
                if(j == 0 || j == i) {
                    list.add(1);
                }
                else {
                    int a = result.get(i - 1).get(j - 1);
                    int b = result.get(i - 1).get(j);
                    list.add(a + b);
                }
            }
            result.add(list);
         }
        return result;
      }
}