118. Pascal's Triangle

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]
]

分析 第k层有k个元素，每层第一个及最后一个元素值为1，对于(k>2)层，第n(n>1 && n < k)个元素A[k][n] = A[k-1][n-1]+A[k-1][n];

 1 class Solution {
 2 public:
 3     vector<vector<int>> generate(int numRows) {
 4         vector<vector<int>> vals;
 5         
 6         vals.resize(numRows);
 7         
 8         for(int i = 0; i < numRows; i++){
 9             vals[i].resize(i+1);
10             vals[i][0] = 1;
11             vals[i][vals[i].size()-1] = 1;
12             for(int j = 1; j < vals[i].size()-1; j++){
13                 vals[i][j] = vals[i-1][j-1]+vals[i-1][j];
14             }
15         }
16         return vals;
17     }
18 };