[Leetcode 35] 118 Pascal's Trangle

Problem:

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]
]

Analysis:

There two ways to solve the problem, either compute each row element separately or use inductive method.

The latter cost much more less, so we use the latter one.

 

Code:

 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         vector<vector<int> > res;
 7         vector<int> tmp;
 8         
 9         if (numRows == 0) return res;
10         if (numRows == 1) {
11             tmp.push_back(1);
12             res.push_back(tmp);
13             return res;
14         }
15         
16         tmp.push_back(1);
17         res.push_back(tmp);
18         tmp.push_back(1);
19         res.push_back(tmp);
20         
21         for (int i=2; i<numRows; i++) {
22             vector<int> next;
23             next.push_back(1);
24             for (int j=1; j<i; j++) {
25                 next.push_back(tmp[j-1] + tmp[j]);
26             }
27             next.push_back(1);
28             
29             res.push_back(next);
30             tmp = next;
31         }
32         
33         return res;
34     }
35 };
View Code

 

Attention:

posted on 2013-05-24 05:39  freeneng  阅读(200)  评论(0)  编辑  收藏  举报

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