Pascal’s Triangle

Problem

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:

Constraints

• 1 <= numRows <= 30

Solution

The problem Pascal's Triangle can be solved intuitively by allocating the sum of the two numbers directly above to each index in array.

Implementation

class Solution
{
  public:
    vector<vector<int>> generate(int numRows)
    {
        vector<vector<int>> ret;
        for (int i = 0; i < numRows; i++)
        {
            vector<int> row(i + 1, 1);
            for (int j = 1; j < i; j++)
                row[j] = ret[i - 1][j - 1] + ret[i - 1][j];
            ret.push_back(row);
        }
        return ret;
    }
};