118. Pascal's Triangle

难度: Easy

题目描述

Given an integer numRows, return the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:

 

Example 1:

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

Example 2:

Input: numRows = 1
Output: [[1]]

 

Constraints:

• 1 <= numRows <= 30

解题思路

代码实现

解决方案

java

class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> result = new ArrayList<>();
       
        for (int i = 1; i <= numRows; i++) {
              List< Integer> cur = new ArrayList<>();
              for(int j=1;j<=i;j++){
                if(j==1||j==i){
                    cur.add(1);
                }else{
                   List<Integer> pre =  result.get(i-2);
                   cur.add(pre.get(j-2)+pre.get(j-1));
                }
              }
              result.add(cur);

        }

        return result;
    }
}