# 36. 杨辉三角

java

```java
import java.util.ArrayList;
import java.util.List;

/**
 * 118. 杨辉三角
 * 给定一个非负整数 numRows，生成杨辉三角的前 numRows 行。
 *
 *
 *
 * 在杨辉三角中，每个数是它左上方和右上方的数的和。
 *
 * 示例:
 *
 * 输入: 5
 * 输出:
 * [
 *      [1],
 *     [1,1],
 *    [1,2,1],
 *   [1,3,3,1],
 *  [1,4,6,4,1]
 * ]
 *
 */
public class Solution188 {

    /**
     * 第一行、二行单独处理
     * 其他行：
     * 1.第0列、第n-1列为1
     * 2.v[n][t]=v[n-1][t]+v[n-1][t+1]
     * (n:行,从0开始;t:第n行的第二个元素t=0，第三个为t=1)
     * @param numRows
     * @return
     */
    public List<List<Integer>> generate(int numRows) {
        int i=3;
        List<List<Integer>> r=new ArrayList<>();
        if (numRows<=0) return r;

        List<Integer> list1=new ArrayList<>();
        list1.add(1);
        r.add(list1);
        if(numRows==1) return r;

        List<Integer> list2=new ArrayList<>();
        list2.add(1);
        list2.add(1);
        r.add(list2);
        if(numRows==2) return r;

        List<Integer> pre=list2;

        while (i<=numRows){
            List<Integer> list=new ArrayList<>();
            r.add(list);
            list.add(1);
            int t=0;
            while(t<i-2){
                list.add(pre.get(t)+pre.get(t+1));
                t++;
            }
            list.add(1);
            pre=list;
            i++;
        }
        return r;
    }

    public static void main(String[] args) {
        int numRows = 5;
        List<List<Integer>> r = new Solution188().generate(numRows);
        System.out.println(r);
    }
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://im-qianuxn.gitbook.io/pytorch/ji-suan-ji/shua-ti/zhi-shang-lei/36-yang-hui-san-jiao.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.