[leetcode.com]算法题目

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]
]

 1 class Solution {
 2 public:
 3     vector<vector<int> > generate(int numRows) {
 4         // Start typing your C/C++ solution below
 5         // DO NOT write int main() function
 6         if(0 == numRows){
 7             vector<vector<int> > result;
 8             return result;
 9         } 
10              
11         vector<vector<int> > result(numRows);
12         
13         vector<int> first(1,1);
14         result[0] = first;
15         for(int i=1;i<numRows;i++){
16             result[i] = nextTriangle(result[i-1]);
17         }
18         
19         return result;    
20     }
21     
22     vector<int> nextTriangle(vector<int> a){
23         int k = a.size();
24         vector<int> next(k+1);
25         for(int i=0;i<k+1;i++){
26             if(0==i){
27                 next[i] = a[i];
28                 continue;
29             }
30             if(k==i){
31                 next[i] = a[k-1];
32                 continue;
33             }
34             next[i] = a[i-1]+a[i];
35         }
36         return next;
37     }
38 };

我的答案

思路：创建一个函数，使用上一行的vector去计算下一行的vector，然后反复调用即可。需要尤其注意输入的值为0时候的情况。