# Java foundation — printing Yang Hui triangle

problem: print out a 10-line yanghui triangle
point: two-dimensional array
idea: first analyze the law of yanghui triangle: 1. 2. Each line ends with a 1; 3. Starting from the third row, every non-first and last number is: yangHui[I][j]=yangHui[i-1][j-1]+yangHui[i-1][j]. The code is:

``````//        1.声明初始化二维数组
int[][] yangHui = new int[10][];
//        2.给数组的元素赋值
for (int i = 0; i < yangHui.length; i++) {
yangHui[i] = new int[i+1];
//            2.1 给首末元素赋值
yangHui[i][0] = 1;
yangHui[i][i] = 1;
//            2.2 给每行的非首末元素赋值
if (i>1){
for (int j = 1; j <yangHui[i].length-1 ; j++) {
yangHui[i][j]=yangHui[i-1][j-1]+yangHui[i-1][j];
}
}
}

//        3.遍历二维数组
for (int i = 0; i < yangHui.length; i++) {
for (int j = 0; j <yangHui[i].length ; j++) {
System.out.print(yangHui[i][j]+"\t");
}
System.out.println();
}
``````

Output:

1 1 1 2 1 1 3 3 1

1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
1 7 21 35 35 21 7 1
1 8 28 56 70 56 28日8 1
1 9 36 84 126 126 84 36 9 1