Pascal's Triangle

Pascal's Triangle

GivennumRows, generate the firstnumRows of Pascal's triangle.

For example, givennumRows = 5,
Return

[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

Answer:

利用杨辉三角中，如下图特性，实现输出杨辉三角。

另附上杨辉三角其它特性。 http://www.mathsisfun.com/pascals-triangle.html

代码实现：

class Solution
{
public:
	vector<vector<int> > generate(int numRows)
	{
		vector<vector<int>> pascalTriangle;
		for (int i = 0; i < numRows; i++)
		{
			vector<int> v;

			//第1行
			if (i == 0)
				v.push_back(1);
			//非第1行
			else
			{
				v.push_back(1);
				for (unsigned int j = 0; j < pascalTriangle[i - 1].size() - 1; j++)
				{
					v.push_back(pascalTriangle[i - 1][j] + pascalTriangle[i - 1][j + 1]);
				}
				//最一列最后一个数为1
				v.push_back(1);
			}
			pascalTriangle.push_back(v);
		}
		return pascalTriangle;
	}

	void printPascalTriangle(vector<vector<int>> pascalTriangle)
	{
		cout << "[" << endl;
		for (unsigned int i = 0; i < pascalTriangle.size(); i++)
		{
			//前面空格
			for (int j = pascalTriangle.size() - i; j > 0; j--)
			{
				cout << " ";
			}

			//输出数字
			cout << "[";
			for (unsigned int j = 0; j < pascalTriangle[i].size() - 1; j++)
			{
				cout << pascalTriangle[i][j] << ",";
			}

			//最后一行
			if (i == pascalTriangle.size() - 1)
			{
				cout << pascalTriangle[i][i] << "]" << endl;
			}

			//非最后一行
			else
				cout << pascalTriangle[i][i] << "]," << endl;
		}
		cout << "]";
	}
};

另过程中遇见Warming: “<" 有符号/无符号不匹配。

原因是因为 vector.size() 返回 unsigned int. 故遍历时， 同样定义 unsigned int  即可。