題目

Given a pattern and a string s, find if s follows the same pattern.

Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in s.

題意

給定一個模式和字串，判斷字串是否有遵循相同的模式。

Example 1:

Input: pattern = "abba", s = "dog cat cat dog"
Output: true

Example 2:

Input: pattern = "abba", s = "dog cat cat fish"
Output: false

Example 3:

Input: pattern = "aaaa", s = "dog cat cat dog"
Output: false

Example 4:

Input: pattern = "abba", s = "dog dog dog dog"
Output: false

解題想法

每個pattern的字元，只能對應到一個字串，屬於一對一個關係。
a跟b不能同時對應dog，
a也不能同時對應到dog跟cat。
首先要先建立模式對應字串與字串對應模式的對照表。
若對照表中沒有相對應的值就加入表中，若有對應值，則比較目前取得的值是否跟對應值相等。

Solution

var wordPattern = function (pattern, str) {
  let matchPattern = {};
  let matchStr = {};
  let strArray = str.split(' ');
  let strLen = strArray.length;

  if (pattern.length !== strLen) {
    return false;
  }

  for (let i = 0; i < strLen; i++) {
    let p = pattern.charAt(i);
    let s = strArray[i];

    if (!matchPattern[p]) {
      matchPattern[p] = s;
    } else if (matchPattern[p] !== s) {
      return false;
    }

    if (!matchStr[s]) {
      matchStr[s] = p;
    } else if (matchStr[s] !== p) {
      return false;
    }
  };
  return true;
}