LeetCode Pascal's Triangle

题目

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]]

C(N,i)的展开，简单地按层递推，逐层展开即可。

代码：

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