118. Pascal's Triangle

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118. Pascal's Triangle

题目

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]
]

解析

• 前面的特殊情况可以放在循环当中处理。

class Solution_118 {
public:
	vector<vector<int>> generate(int numRows) {
		vector<vector<int>> vecs;
		vector<int> vec;
		if (numRows==0)
		{
			return vecs;
		}
		//if (numRows==1)  //放在循环中
		//{
		//	vec.push_back(1);
		//	vecs.push_back(vec);
		//	return vecs;
		//}
		//if (numRows == 2)
		//{
		//	vec.push_back(1);
		//	vecs.push_back(vec);
		//	vec.clear();
		//	vec.push_back(1);
		//	vec.push_back(1);
		//	vecs.push_back(vec);
		//	
		//	return vecs;
		//}
		//vec.push_back(1);
		//vecs.push_back(vec);
		//vec.clear();
		//vec.push_back(1);
		//vec.push_back(1);
		//vecs.push_back(vec);
		//vec.clear();
		for (int i = 1; i <= numRows;i++)
		{
			vec.resize(i,1);   //vector<int> tmp(i,1);
			for (int j = 1; j < vec.size()-1; j++)
			{
				vec[j] = vecs[i - 2][j - 1] + vecs[i - 2][j];
			}
			vecs.push_back(vec);
		}

		return vecs;
	}
};

题目来源

• 118. Pascal's Triangle