valid-word-square.js

/**
 * Valid Word Square
 *
 * Given a sequence of words, check whether it forms a valid word square.
 *
 * A sequence of words forms a valid word square if the kth row and column read the exact same string,
 * where 0 ≤ k < max(numRows, numColumns).
 *
 * Note:
 * 1. The number of words given is at least 1 and does not exceed 500.
 * 2. Word length will be at least 1 and does not exceed 500.
 * 3. Each word contains only lowercase English alphabet a-z.
 *
 * Example 1:
 *
 * Input:
 * [
 *   "abcd",
 *   "bnrt",
 *   "crmy",
 *   "dtye"
 * ]
 *
 * Output:
 * true
 *
 * Explanation:
 * The first row and first column both read "abcd".
 * The second row and second column both read "bnrt".
 * The third row and third column both read "crmy".
 * The fourth row and fourth column both read "dtye".
 *
 * Therefore, it is a valid word square.
 *
 * Example 2:
 *
 * Input:
 * [
 *   "abcd",
 *   "bnrt",
 *   "crm",
 *   "dt"
 * ]
 *
 * Output:
 * true
 *
 * Explanation:
 * The first row and first column both read "abcd".
 * The second row and second column both read "bnrt".
 * The third row and third column both read "crm".
 * The fourth row and fourth column both read "dt".
 *
 * Therefore, it is a valid word square.
 *
 * Example 3:
 *
 * Input:
 * [
 *   "ball",
 *   "area",
 *   "read",
 *   "lady"
 * ]
 *
 * Output:
 * false
 *
 * Explanation:
 * The third row reads "read" while the third column reads "lead".
 *
 * Therefore, it is NOT a valid word square.
 */

/**
 * @param {string[]} words
 * @return {boolean}
 */
const validWordSquare = words => {
  for (let i = 0; i < words.length; i++) {
    for (let j = 0; j < words[i].length; j++) {
      // (j >= words.length) means the the number of rows is too small
      // (i >= words[j].length) means the word at j-th row is too short
      if (j >= words.length || i >= words[j].length || words[i][j] !== words[j][i]) {
        return false;
      }
    }
  }

  return true;
};

export { validWordSquare };