How to use PHP to output a Yang Hui triangle

Yang Hui's triangle is composed of positive integers, and the numbers are symmetrical. Each row starts from 1 and gradually becomes larger, then becomes smaller, and returns to 1; each number in Yang Hui's triangle is its upper left We can understand it as the sum of the square and the number in the upper right corner as a two-dimensional array, which outputs the data through two loops.

1. What is Yang Hui Triangle?

Yang Hui triangle is a way of writing binomial coefficients. Because the arrangement shape is similar to a triangle, it is called Yang Hui triangle.
Yang Hui’s triangle is composed of positive integers, and the numbers are symmetrical. Each row starts from 1 and gradually becomes larger, then becomes smaller, and returns to 1; each number in Yang Hui’s triangle is the sum of the numbers in its upper left and upper right. We can understand it as a two-dimensional array and output the data through two loops.

2. How to use PHP to achieve it?

We can create a new array to store the array elements output through the loop, customize a function to implement this function, and finally implement it by calling the function.

<?php
function triangle($n){
  $arr = array();
  //使用嵌套的for循环来输出二维数组元素
  for($i = 1;$i <= $n;$i++){
    for($j = 1;$j <= $i;$j++){
      if($i == 1 || $i == $j){
        //循环打印前两行
        echo $arr[$i][$j] = 1;
      }else{
        //循环打印后面的行
        echo $arr[$i][$j] = $arr[$i-1][$j-1] + $arr[$i-1][$j];
      }
        echo "  ";
    }
    echo "<br/>";
}
/通过调用自定义函数来打印10行的杨辉三角
triangle(10);
?>

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