I want to print diamond pattern using *. Please find the code below:

for (let i=0; i<num; i  ) {
    let str="";
    for (let j=i; j<num; j  ) {
        str ="*";
    }
    console.log(str);
}

for (let i=num; i>0; i--) {
    let spaces=num-i;
    let spacesStr="";
    for (let j=0; j<spaces; j  ) {
        spacesStr =" ";
    }
    let str=spacesStr;
    for (let j=i; j>0; j--) {
        str ="*";
    }
    console.log(str);
}

The output of the above code is as below:

****
***
**
*
****
 ***
  **
   *

I know that if I start printing both the patterns from line 1 I can achieve the desired output. But not sure how I can do that. Please let me know.

thanks

CodePudding user response：

You've quite figured out the answer already. You will need 3 for loops inside your main loop inorder to get that pattern.

let num = 5;
let string = "";

for (let i = 0; i <= num; i  ) {
  // printing star
  for (let j = 0; j < num - i; j  ) {
    string  = "*";
  }
  // printing spaces
  for (let k = 0; k < i * 2; k  ) {
    string  = " ";
  }

  // printing stars
  for (let l = num - i; l > 0; l--) {
    string  = "*";
  }
  string  = "\n";
}

console.log(string);

First, we print the left stars, then we print the spaces, and then again we print the right stars.

CodePudding user response：

The idea is to build each line.

First, let's focus on the top half of the diamond.

• On the first line, there are n stars, 0 spaces, n stars.
• On the second line, there are n-1 stars, 2 spaces, n-1 stars.
• On the third line, there are n-2 stars, 4 spaces, n-2 stars.
• And the pattern follows till there are 0 stars.

Now, coming to the bottom half of the diamond, the pattern is same, just reversed. So, for the inner loops, you can just change i to n-i and n-i to i.

const n = 5;
const star = "*";
const space = " ";

// Top half of the diagram
for (let i = 0; i < n; i   ) {
  let pattern = ''
  for (let j = 0; j < (n - i); j  ) pattern  = star;
  for (let j = 0; j < i; j  ) pattern  = `${space}${space}`;
  for (let j = 0; j < (n - i); j  ) pattern  = star;
  console.log(pattern);
}

// Bottom half of the diagram
for (let i = 1; i <= n; i   ) {
  let pattern = ''
  for (let j = 0; j < i; j  ) pattern  = star;
  for (let j = 0; j < (n - i); j  ) pattern  = `${space}${space}`;
  for (let j = 0; j < i; j  ) pattern  = star;
  console.log(pattern);
}