0028. Implement strStr().js

// Implement strStr().
//
// Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
//
// Example 1:
//
// Input: haystack = "hello", needle = "ll"
// Output: 2
//
// Example 2:
//
// Input: haystack = "aaaaa", needle = "bba"
// Output: -1
//
// Clarification:
//
// What should we return when needle is an empty string? This is a great question to ask during an interview.
//
// For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

/**
 * @param {string} haystack
 * @param {string} needle
 * @return {number}
 */

/** 1) Cheating */
const strStr1 = (haystack, needle) => {
  if (needle == null || needle === '') return 0;
  return haystack.indexOf(needle);
};

/** 2) Brute force */
const strStr2 = (haystack, needle) => {
  if (needle == null || needle === '') return 0;
  for (let i = 0; i < haystack.length - needle.length + 1; i++) {
    if (haystack.substr(i, needle.length) === needle) return i;
  }
  return -1;
};

/** 3) Same to 2) */
const strStr = (haystack, needle) => {
  if (needle == null || needle === '') return 0;
  for (let i = 0; i < haystack.length - needle.length + 1; i++) {
    for (let j = 0; j < needle.length; j++) {
      if (haystack[i + j] !== needle[j]) break;
      if (j === needle.length - 1) return i;
    }
  }
  return -1;
};

/** 4) KMP */
// https://www.zhihu.com/question/21923021