[Algorithm] Reverse array of Chars by word

For example we have:

["p", "r", "e", "f", "e", "t", " ", "m", "a", "k", "e", " ", "p", "r", "a", "t", "i", " c", "e"]

We want to get:

["p", "r", "a", "t", "i", " c", "e", " ", "m", "a", "k", "e", " ", "p", "r", "e", "f", "e", "t"]

 

Requirement:

　　You can only do in array swap, you cannot create a new array.

 

The way to do it:

　　1. Reverse whole string to get:

["e", " c", "i", "t", "a", "r", "p", " ", "e", "k", "a", "m", " ", "t", "e", "f", "e", "r", "p"]

　　2. Then we reverse each word to get final result:

["p", "r", "a", "t", "i", " c", "e", " ", "m", "a", "k", "e", " ", "p", "r", "e", "f", "e", "t"]

 

So the main function should looks like this:

let data = [
  "p","r","e","f","e","t"," ",
  "m","a","k","e"," ",
  "p","r","a","t","i","c","e"
];

function main(_data) {
  let data = _data.slice();

  reverseWholeString(data);
  reverseWords(data, 0);

  return data;
}

console.log(main(data));

 

The reverseWholeString function would be:

function reverseWholeString(data) {
  let start = 0,
    end = data.length - 1;
  reverseChars(data, start, end);
}

function reverseChars(data, start, end) {
  while (start < end) {
    [data[start], data[end]] = [data[end], data[start]];
    start++;
    end--;
  }
}

 

reverseWords function would be:

function reverseWords(data, start) {
  let index = findEmptyIndex(data, start);
  let end = index - 1;

  while (index !== -1) {
    reverseChars(data, start, end);
    start = index + 1;
    index = findEmptyIndex(data, start);
    end = index - 1;
  }

  reverseChars(data, start, data.length - 1);
}

function findEmptyIndex(data, start) {
  let index;
  for (let i = start; i < data.length; i++) {
    if (data[i] === " ") {
      index = i;
      break;
    } else {
      index = -1;
    }
  }

  return index;
}

 

------------

Full code:

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let data = [   "p",   "r",   "e",   "f",   "e",   "t",   " ",   "m",   "a",   "k",   "e",   " ",   "p",   "r",   "a",   "t",   "i",   " c",   "e" ];   function reverseWholeString(data) {   let start = 0,     end = data.length - 1;   reverseChars(data, start, end); }   function reverseChars(data, start, end) {   while (start < end) {     [data[start], data[end]] = [data[end], data[start]];     start++;     end--;   } }   function findEmptyIndex(data, start) {   let index;   for (let i = start; i < data.length; i++) {     if (data[i] === " ") {       index = i;       break;     } else {       index = -1;     }   }     return index; } function reverseWords(data, start) {   let index = findEmptyIndex(data, start);   let end = index - 1;     while (index !== -1) {     reverseChars(data, start, end);     start = index + 1;     index = findEmptyIndex(data, start);     end = index - 1;   }     reverseChars(data, start, data.length - 1); }   function main(_data) {   let data = _data.slice();     reverseWholeString(data);   reverseWords(data, 0);     return data; }   console.log(main(data));