@requires_authorization

@author johnsondu

@create_time 2015.7.23 19:54

@url [Pascal's Triangle](https://leetcode.com/problems/pascals-triangle/)

/************************

 * @description: simple.

 * @time_complexity:  O(n)

 * @space_complexity: O(n)

 ************************/

 class Solution {

public:

    vector<vector<int>> generate(int numRows) {

        vector<vector<int>> ans;

        for(int i = 1; i <= numRows; i ++) {

            vector<int> layer;

            if(i == 1) layer.push_back(1);

            else {

                for(int j = 1; j <= i; j ++) {

                    if(j == 1 || j == i)  layer.push_back(1);

                    else layer.push_back(ans[i-2][j-2] + ans[i-2][j-1]);

                }

            }

            ans.push_back(layer);

        }

        return ans;

    }

};

@requires_authorization

@author johnsondu

@create_time 2015.7.23 19:54

@url [Pascal's Triangle](https://leetcode.com/problems/pascals-triangle/)

/************************

 * @description: simple.

 * @time_complexity:  O(n)

 * @space_complexity: O(n)

 ************************/

class Solution {

public:

    vector<vector<int>> generate(int numRows) {

        vector<vector<int>> ans;

        if(numRows < 1) return ans;

        vector<int> first;

        first.push_back(1);

        ans.push_back(first);

        if(numRows < 2) return ans;

        vector<int> second;

        second.push_back(1);

        second.push_back(1);

        ans.push_back(second);

        for(int i = 3; i <= numRows; i ++) {

            vector<int> layer;

            layer.push_back(1);

            for(int j = 0; j < ans[i-2].size()-1; j ++) {

                layer.push_back(ans[i-2][j] + ans[i-2][j+1]);

            }

            layer.push_back(1);

            ans.push_back(layer);

        }

        return ans;

    }

};