使用 javascript 将字符串从 aaabccdd 解密为 a3b1c2d2？

Question

我试过这种方法，但没有得到字符串的第一个元素。我试图以相反的方式进行转换，这太容易了。但在这一个不知何故我错过了一些东西。问题是，我们需要破译从“aabbcdd”到“a2”的字符串 b2c1d2

function check(len, string){
    // var obj = {};
    var new_string = "";
    var count =1;
    //console.log(string);
    for(var i=0; i < string.length; i++){
        let str = string[i];
        if(string[i]===string[i+1] ){
            count++;
            new_string = new_string + string[i+1] + count;
        }
        if(string[i]!== string[i-1] && string[i]!== string[i+1] && string[i-1] !==undefined){
            count = 1;
            new_string  = new_string + string[i-1] + count;
        }
        
        
        // console.log(string[i],string[i+1], count)
        
    }
    console.log(new_string);
}

谢谢

Answer 1

您需要以不同于其他字符的方式处理字符串的第一个字符，并且您还需要在处理完最后一个字符后再次更新字符串。

这里有一个评论很多的例子，演示了如何做到这一点。如果有什么不清楚的地方，请随时在评论中要求澄清。

You might find it useful to reference string iterators on MDN.

TS Playground

// Regular expression used to validate each unit (character) of the string
// in the following function, but we instantiate it once instead of
// every time the function is called
const lowerAlphaCharacterRegex = /^[a-z]$/;

// Validate the expected character
function validate (str) {
  if (!lowerAlphaCharacterRegex.test(str)) throw new Error('Invalid input');
}

function encode (input) {
  let result = '';

  // Get an interator for the string to handle each unit
  const iter = input[Symbol.iterator]();
  // Get the first unit and assign it to the working character state
  let previous = iter.next().value;
  // Validate that it meets the criteria
  validate(previous);
  // Set the intiial count to 1
  let count = 1;

  // Iterate over the remaining units in the string
  for (const char of iter) {
    // Validate that it meets the criteria
    validate(char);

    // Simply update the count and continue to the next loop iteration
    // if the current character is the same as the previous one
    if (char === previous) {
      count += 1;
      continue;
    }

    // Otherwise...

    // Update the result
    result += `${previous}${count}`;

    // Update the character state
    previous = char;
    count = 1;
  }

  // Update the result from the remaining state
  result += `${previous}${count}`;

  return result;
}

const input = 'aabbcdd';
const expected = 'a2b2c1d2';
const actual = encode(input);

console.log({
  actual,
  valid: actual === expected,
});

使用 javascript 将字符串从 aaabccdd 解密为 a3b1c2d2？

Using javascript decipher a string from aaabccdd to a3b1c2d2?

javascript

node.js

string

run-length-encoding