118. Pascal's Triangle

118. Pascal's Triangle (Easy)

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

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

Example:

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

Companies:
Bloomberg, Google, Facebook

Solution 1.

// OJ: https://leetcode.com/problems/pascals-triangle/
// Author: github.com/lzl124631x
// Time: O(N^2)
// Space: O(1)
class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> ans(numRows);
        for (int i = 0; i < numRows; ++i) {
            ans[i] = vector<int>(i + 1, 1);
            for (int j = 1; j < i; ++j) ans[i][j] = ans[i - 1][j - 1] + ans[i - 1][j];
        }
        return ans;
    }
};