14. Longest Common Prefix

Problem:

Write a function to find the longest common prefix string amongst an array of strings.

If there is no common prefix, return an empty string "".

Example 1:

Input: ["flower","flow","flight"]
Output: "fl"

Example 2:

Input: ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.

Note:

All given inputs are in lowercase letters a-z.

Solution:

ONE

JavaScript specific solution. Get the min len then narrow down the prefix.

/**
 * @param {string[]} strs
 * @return {string}
 */
let longestCommonPrefix = function (strs) {
  if (strs.length > 0) {
    let minLen = Math.min(...strs.map((s) => s.length));
    const anyStr = strs[0];
    while (minLen) {
      const prefix = anyStr.slice(0, minLen--);
      if (strs.every((s) => s.startsWith(prefix))) {
        return prefix;
      }
    }
  }
  return "";
};

TWO

/**
 * @param {string[]} strs
 * @return {string}
 */
let longestCommonPrefix = function (strs) {
  if (strs.length <= 0) {
    return "";
  }

  let i = 0;
  while (strs.every((s) => s[i] && s[i] === strs[0][i])) {
    i++;
  }
  return strs[0].slice(0, i);
};

THREE

General solution. Build up the prefix.

/**
 * @param {string[]} strs
 * @return {string}
 */
let longestCommonPrefix = function (strs) {
  let prefix = "";
  if (strs.length > 0) {
    for (let i = 0; ; i++) {
      const c = strs[0][i];
      if (!c) {
        return prefix;
      }
      for (let j = 0; j < strs.length; j++) {
        if (strs[j][i] !== c) {
          return prefix;
        }
      }
      prefix += c;
    }
  }
  return prefix;
};

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