118. Pascals Triangle¶

Difficulty: Easy

118. Pascal's Triangle

Easy

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]]

Example 2:

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

Constraints:

1 <= numRows <= 30

Solution¶

class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> ans = new ArrayList<>();
        List<Integer> temp = null;
        for (int i=0; i< numRows; i++) {
            List<Integer> row = new ArrayList<>();
            for (int j = 0;j <= i; j++) {
                if (j == 0 ||j == i){
                    row.add(1);
                }
                else {
                    row.add(temp.get(j - 1) + temp.get(j));
                }
            }
            temp = row;
            ans.add(row);
        }
        return ans;
    }
}

Complexity Analysis¶

Time Complexity: O(?)
Space Complexity: O(?)

Approach¶

Detailed explanation of the approach will be added here