The Solution to Leetcode 118 Pascal's Triangle

Question:

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]
]

思路：由上述例子可以看出，元素之间满足这样的一个关系：a[i][j]=a[i-1][j-1]+a[i-1][j]，除了每一行的第一个数和最后一个数都是1以外。

Answer:

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

run code results:

Your input

5

Your answer

[[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

Expected answer

[[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]