text: /**
   * Problem: Longest Common Prefix
   * Difficulty: Easy
   * Runtime: 52 ms
   * Date: 2018/04/02
   * Author: Aonan He
   */
  /**
   * @param {string} haystack
   * @param {string} needle
   * @return {number}
   */
  var strStr = function (haystack, needle) {
      const len = haystack.length - needle.length
      for (let i = 0; i <= len; i++) {
          if (haystack.substring(i, i + needle.length) === needle) {
              return i
          }
      }
      return -1
  };
  