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]
]

也是一体基本的DP题吧：

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

贴上一个更加简洁的方法：

class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        vector<vector<int>> r(numRows);

        for (int i = 0; i < numRows; i++) {
            r[i].resize(i + 1);
            r[i][0] = r[i][i] = 1;
  
            for (int j = 1; j < i; j++)
                r[i][j] = r[i - 1][j - 1] + r[i - 1][j];
        }
        
        return r;
    }
};