[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:

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));