【leetcode】Pascal’s Triangle

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]]

Anwser 1：      

class Solution {public:    vector<vector<int> > generate(int numRows) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector< vector<int> > ret;                for(int i = 0; i < numRows; i++){            vector<int> tmp;            tmp.clear();            if(i == 0) {                tmp.push_back(1);                ret.push_back(tmp);                continue;            }                        for(int j = 0; j <= i; j++){                if(j == 0) {                    tmp.push_back(1);                } else if(i == j){                    tmp.push_back(1);                } else {                    tmp.push_back( ret[i-1][j-1] + ret[i-1][j] );   // last row                }            }            ret.push_back(tmp);        }                return ret;    }};