118. Pascal's Triangle

• Difficulty: Easy

• Topics: Array

• Similar Questions:

  • Pascal's Triangle II

Problem:

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]
]

Solutions:

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> ret;
        if (numRows < 1)    return ret;
        ret.push_back({1});

        for (int i = 1; i < numRows; ++i) {
            vector<int> row (i + 1, 1);
            for (int j = 1; j < i; ++j) {
                row[j] = ret.back()[j-1] + ret.back()[j];
            }
            ret.push_back(row);
        }

        return ret;
    }
};