118. Pascal's Triangle

 

Given a non-negative integer  numRows , generate the first  numRows  of Pascal’s triangle.


In Pascal’s triangle, each number is the sum of the two numbers directly above it.

Example:

Input: 5
Output:
[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]


  
  

杨辉三角是二项式系数的一种写法,如果熟悉杨辉三角的五个性质,那么很好生成,可参见我的上一篇博文Pascal’s Triangle II。具体生成算是:每一行的首个和结尾一个数字都是1,从第三行开始,中间的每个数字都是上一行的左右两个数字之和。代码如下:

 

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

 

类似题目:

Pascal’s Triangle II

 

参考资料:

https://leetcode.com/problems/pascals-triangle/

https://leetcode.com/problems/pascals-triangle/discuss/38150/My-C%2B%2B-code-0ms

 

LeetCode All in One 题目讲解汇总(持续更新中…)


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