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];

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> vals;
        
        vals.resize(numRows);
        
        for(int i = 0; i < numRows; i++){
            vals[i].resize(i+1);
            vals[i][0] = 1;
            vals[i][vals[i].size()-1] = 1;
            for(int j = 1; j < vals[i].size()-1; j++){
                vals[i][j] = vals[i-1][j-1]+vals[i-1][j];
            }
        }
        return vals;
    }
};