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1v.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elsecout << 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。