How to write a state machine to solve the Count the smiley faces?-CodePudding

I have solved the problem Conunt the smiley faces, then when I look through the solutions I find that many people use regexp. Then I want write a state machine to implement regexp and solve this problem. But I failed. This is my code:

function countSmileys(smileys) {
  let state = smileyHasValidEye;
  return smileys.filter(smiley => {
    for (let s of [...smiley]) {
      state = state(s);
    }
    return state === true;
  }).length;
}

function smileyHasValidEye(s) {
  if (s === ':' || s === ';') {
    return smileyHasValidNose;
  }
  return smileyHasValidEye;
}

function smileyHasValidNose(s) {
  if (s === '-' || s === '~') {
    return smileyHasValidMouth;
  }
  return smileyHasValidMouth(s);
}

function smileyHasValidMouth(s) {
  if (s === ')' || s === 'D') {
    return true;
  }
  return;
}

console.log(countSmileys([':)', ';(', ';}', ':-D']));

state = state(s);
              ^

TypeError: state is not a function

Then I debugged my code I found the procedure doesn't enter the smileyHasValidNose function. Then I don't know the reason.

CodePudding user response：

The problem is you don't really reset state in between smileys. So the next smiley state will be true which you can't call (it's not a function).

You could use a local variable for state that resets it to the first function (the first step).

function countSmileys(smileys) {
  let firstStep = smileyHasValidEye;
  return smileys.filter(smiley => {
    let state = firstStep;
    for (let s of [...smiley]) {
      state = state(s);
    }
    return state === true;
  }).length;
}

function smileyHasValidEye(s) {
  if (s === ':' || s === ';') {
    return smileyHasValidNose;
  }
  return smileyHasValidEye;
}

function smileyHasValidNose(s) {
  if (s === '-' || s === '~') {
    return smileyHasValidMouth;
  }
  return smileyHasValidMouth(s);
}

function smileyHasValidMouth(s) {
  if (s === ')' || s === 'D') {
    return true;
  }
  return;
}

console.log(countSmileys([':)', ';(', ';}', ':-D']));

This code however, will error if there's more on the string besides the smiley (or a partial of the smiley).

I would change smileyHasValidMouth to return false if it doesn't detect a smiley. Just to be more consistent here...

function smileyHasValidMouth(s) {
  if (s === ')' || s === 'D') {
    return true;
  }
  return false;
}

And adjust your loop to exit early if it finds a value that is not a function.

    for (let s of [...smiley]) {
      state = state(s);
      if(typeof state !== 'function') return state;
    }

function countSmileys(smileys) {
  let firstStep = smileyHasValidEye;
  return smileys.filter(smiley => {
    let state = firstStep;
    for (let s of [...smiley]) {
      state = state(s);
      if (typeof state !== 'function') return state;
    }
  }).length;
}

function smileyHasValidEye(s) {
  if (s === ':' || s === ';') {
    return smileyHasValidNose;
  }
  return smileyHasValidEye;
}

function smileyHasValidNose(s) {
  if (s === '-' || s === '~') {
    return smileyHasValidMouth;
  }
  return smileyHasValidMouth(s);
}

function smileyHasValidMouth(s) {
  if (s === ')' || s === 'D') {
    return true;
  }
  return false;
}

console.log(countSmileys([':~(', ':>', ':D', ':(', ':o>', ';)', ':)']));