[LeetCode] Pascal's Triangle

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]] 问题描述：给定一个整数numRows，生成Pascal三角形的前numRows行。将该三角形的左边对齐，就能够发现，tri[i][j] = tri[i-1][j-1] + tri[i-1][j]。
class Solution {public:    vector<vector<int> > generate(int numRows) {        // Note: The Solution object is instantiated only once and is reused by each test case.        if(numRows == 0)            return vector<vector<int> >(0);        vector<vector<int> > ivec;        int i = 0, j = 0;        for(i = 0; i < numRows; i++) {            vector<int> vec;            for(j = 0; j < i+1; j++) {                if(j == 0 || j == i)                    vec.push_back(1);                else                    vec.push_back(ivec[i-1][j-1] + ivec[i-1][j]);            }            ivec.push_back(vec);        }        return ivec;    }};