LeetCode OJ

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]
]

解题思路：

直接求解杨辉三角

代码：

class Solution {
public:
    vector<vector<int> > generate(int numRows) {
        vector<vector<int>> ans;
        if (numRows == 0) return ans;
        
        vector<int> row_one;
        vector<int> row_two;
        
        for (int i = 1; i <= numRows; i++) {
            if (i & 1) {
                for (int j = 0; j < i; j++) {
                    if (j == 0 || j == i-1) {
                        row_one.push_back(1);
                    }else {
                        row_one.push_back(row_two[j-1] + row_two[j]);
                    }
                }
                row_two.erase(row_two.begin(), row_two.end());
                ans.push_back(row_one);
            } else {
                for (int j = 0; j < i; j++) {
                    if (j == 0 || j == i-1) {
                        row_two.push_back(1);
                    }else {
                        row_two.push_back(row_one[j-1] + row_one[j]);
                    }
                }
                row_one.erase(row_one.begin(), row_one.end());
                ans.push_back(row_two);
            }
        }
        
        return ans;
    }
};