Title:
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] ]
递归:
class Solution { public: vector<vector<int> > results; vector<vector<int>> generate(int numRows) { if (numRows < 1) return results; maker(numRows); return results; } void maker(int numRows){ vector<int> cur; cur.push_back(1); if (numRows == 2){ maker(numRows-1); cur.push_back(1); } else if (numRows > 2){ maker(numRows-1); vector<int> pre = results[numRows-2]; for (int i = 0 ; i < pre.size()-1; i++){ cur.push_back(pre[i]+pre[i+1]); } cur.push_back(1); } results.push_back(cur); } };
非递归
class Solution { public: vector<vector<int> > results; vector<vector<int>> generate(int numRows) { if (numRows < 1) return results; vector<int> result; result.push_back(1); results.push_back(result); for (int i = 2; i <= numRows; i++){ vector<int> pre = results[i-2]; vector<int> cur; cur.push_back(1); for (int j = 0; j < pre.size()-1; j++){ cur.push_back(pre[j]+pre[j+1]); } cur.push_back(1); results.push_back(cur); } return results; } };
Title:
Given an index k, return the kth row of the Pascal's triangle.
For example, given k = 3,
Return [1,3,3,1]
.
思路:使用滚动数组
class Solution { public: vector<int> getRow(int rowIndex) { vector<int> result; if (rowIndex < 0) return result; result.push_back(1); for (int i = 0; i < rowIndex ; i++){ vector<int> cur; cur.push_back(1); for (int j = 0 ; j < result.size()-1; j++){ cur.push_back(result[j]+result[j+1]); } cur.push_back(1); result = cur; } return result; } };