Pascal's Triangle

07/11/2016 Array

Question
Solution

Question

Given numRows, generate the first numRows of Pascal’s triangle.

For example, given numRows = 5,

Return
[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

Solution

Result: Accepted Time: 3 ms

Here should be some explanations.

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> ans(numRows);
        if(numRows)
            ans[0].push_back(1);
        if(numRows > 1)
        {
            ans[1].push_back(1);
            ans[1].push_back(1);
            for(int i = 2 ;i < numRows;  i++)
            {
                ans[i] = vector<int>(i+1);
                ans[i][0] = 1;
                for(int j=1; j < i; j++)
                    ans[i][j]=ans[i-1][j-1] + ans[i-1][j];
                ans[i][i] = 1;
            }
        }
        return ans;
    }
};

Complexity Analytics

Time Complexity: $O(n)$
Space Complexity: $O(1)$