[Leetcode 35] 118 Pascal's Trangle

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]
]

Analysis:

There two ways to solve the problem, either compute each row element separately or use inductive method.

The latter cost much more less, so we use the latter one.

Code:

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> > res;
        vector<int> tmp;
        
        if (numRows == 0) return res;
        if (numRows == 1) {
            tmp.push_back(1);
            res.push_back(tmp);
            return res;
        }
        
        tmp.push_back(1);
        res.push_back(tmp);
        tmp.push_back(1);
        res.push_back(tmp);
        
        for (int i=2; i<numRows; i++) {
            vector<int> next;
            next.push_back(1);
            for (int j=1; j<i; j++) {
                next.push_back(tmp[j-1] + tmp[j]);
            }
            next.push_back(1);
            
            res.push_back(next);
            tmp = next;
        }
        
        return res;
    }
};

Attention: