JS implements the sample code of decimal conversion to hexadecimal

Preface

When we write code, we occasionally encounter the problem of base conversion. Common conversions include binary, octal, decimal, and hexadecimal, but hexadecimal is rarely heard of. Here, let's use JS to simply try to implement hexadecimal.

think

The structure of hexadecimal numbers

Before we begin, we need to first understand the composition of hexadecimal numbers so that we can have a clear understanding of hexadecimal numbers and the subsequent conversion of numbers. We all know that hexadecimal numbers are composed of characters from 0 to 9 and a to a. So what about hexadecimal numbers? , push af back 20 places, and it is obvious that its letter part is composed of 26 English letters az, so the hexadecimal number is composed of 0-9, az

Numerical preparation

After understanding its composition, start thinking, how can a decimal number be transformed into a hexadecimal number? We need to first prepare a "warehouse" array with 36 values. This array is used to store all the values ​​of hexadecimal numbers. When a decimal number needs to be converted, the value of the hexadecimal number is taken out of the warehouse according to the value. In the warehouse, 0-9 represents 0-9 of the hexadecimal number, and 10-35 represents az of the hexadecimal number. The code is as follows

function getNums36() {
  var nums36 = [];
  for(var i = 0; i < 36 ; i++) {
    if(i >= 0 && i <= 9) { // Store the values ​​0-9 nums36.push(i) 
    } else { // Store the value of az nums36.push(String.fromCharCode(i + 87)); // ASCII code conversion }
  }
  console.log(nums36,'--------'); // Check the value of the warehouse return nums36; 
}

accomplish

After the warehouse is built, we begin the process of decomposing the binary conversion.

• First, the decimal number passed in is tested, and the floating-point number is judged first. Since the base conversion of floating-point numbers is not discussed here, it is returned directly. Secondly, negative numbers are detected and processed. If n is a negative number, the Math.abs() method is called to convert n into a positive number.
• After the detection is completed, the conversion begins

Set up a while loop. First, perform modulo 36 on the value of n to get res.

var res = n % 36;

Here we need to get the lowest bit value of the decimal number converted to hexadecimal, throw res into the warehouse, get the corresponding hexadecimal value, and use unshift to store it in the first bit of arr.

arr.unshift(nums36[res]);

After processing the lowest bit, we need to carry the number and process the value of the higher bit.

n = parseInt(n/36);

At this point, a cycle is completed

We use while to continuously take the modulus of res on n and carry it continuously. Finally, we can convert the decimal number into a hexadecimal number.

Note that at this time, remember to add the negative number judgment of neg set previously to the first place

arr.unshift(neg)

Finally, return the hexadecimal number

return arr.join("");

Code

// Provide 36-bit expression 0-9 az
function getNums36() {
  var nums36 = [];
  for(var i = 0; i < 36 ; i++) {
    if(i >= 0 && i <= 9) {
      nums36.push(i)
    } else {
      nums36.push(String.fromCharCode(i + 87));
    }
  }
  return nums36;
}
function scale36(n) {
  // Single function // Hexadecimal number: 0-9 af Hexadecimal number: 0-9 az   
  const arr = [];
  var nums36 = getNums36();
  // 36 10
  if(!Number.isInteger(n)){//Floating point number judgment, currently does not support mice console.warn('decimal conversion is not supported');
    return n;
  } 
  var neg = '';
  if(n < 0){//Processing of negative numbers neg = '-';
      n = Math.abs(n)
  }
  while(n) {
    var res = n % 36;
    console.log(res,'++++++++');
    arr.unshift(nums36[res]);
    // Carry n = parseInt(n/36);
    console.log(n,'---------');
  }
  arr.unshift(neg)
  return arr.join("");

}

console.log(scale36(20)); // 10

Extensions

Implementation of 7-base numbers

This template is also applicable to the conversion of decimal to other bases. We only need to modify the value of the warehouse. Here we take a 7-base problem of LeetCode as an example

504. Base 7 Given an integer, convert it to base 7 and output it as a string.

Example 1:
Input: 100 Output: "202"

First prepare the 7-base numerical warehouse

function getNums7() {
  var nums7 = [];
  for(var i = 0; i < 7 ; i++) {
    
      nums7.push(i)
   
  }
  return nums7;
}

Then modify the remainder value and carry to complete the template reuse.

var res = n % 7;
n = parseInt(n/7);

Code function getNums7() {
  var nums7 = [];
  for(var i = 0; i < 7 ; i++) {
    
      nums7.push(i)
   
  }
  return nums7;
}
var convertToBase7 = function(num) {
  // Single function const arr = [];
  var nums7 = getNums7();
  var neg = '';
  if(num < 0){//Processing of negative numbers neg = '-';
      num = Math.abs(num)
  }
  if(num == 0) {
      return num + "";
  }
  
  while(num) {
    var res = num % 7; // intercept the high-order data arr.unshift(nums7[res]);  
    // Carry num = parseInt(num/7); 
  }
  arr.unshift(neg);
  return arr.join("");

}

summary

From this example, we can see that with a little modification, we can easily convert the decimal system to other systems. The key lies in the modulo of res and the construction of the warehouse value. By continuously carrying and while looping, we can finally get the number we want.

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