Problem:

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]

]

Summary:

输出杨辉三角的前n行。

Solution:

方法类似于LeetCode 119 Pascal's Triangle II

 class Solution {

 public:

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

         vector<vector<int>> res;

         vector<int> v;

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

             v.resize(i + );

             v[] = v[i] = ;

             for (int j = i - ; j > ; j--) {

                 v[j] = v[j - ] + v[j];

             }

             res.push_back(v);

         }

         return res;

     }

 };

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