LeetCode 118. Pascal's Triangle (Java)

118. Pascal's Triangle

Given a non-negative integer numRows, generation ago with numRows Yang Hui Triangle.
In Pascal's Triangle, each number is the number of its top left and top right and.

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

Source: stay button (LeetCode)
link: https: //leetcode-cn.com/problems/pascals-triangle
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class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> triangle=new ArrayList<List<Integer>>();
        if(numRows==0)
        {
            return triangle;
        }
        triangle.add(new ArrayList<>());
        triangle.get(0).add(1);
        for(int rowNum=1;rowNum<numRows;rowNum++)
        {
            List<Integer> row=new ArrayList<>();
            List<Integer> prevRow = triangle.get(rowNum-1);//前一行的所有元素
            row.add(1);//第一个元素为1
            for(int i=1;i<rowNum;i++)
            {
                row.add(prevRow.get(i-1)+prevRow.get(i));//之后的元素等于其左上角元素加其上方元素
            }
            row.add(1);//最后一个元素为1
            triangle.add(row);//将新一行加入数组中
        }
        return triangle;
    }
}