<aside> ✍️ Key Points:

• 经典题型：

  • Character to Integer Conversion
  • Remove Extra Space
  • Char Removal
  • Reverse
  • Find Permutations (Match)
  • Replace/EnCode/Decode

• 什么时候想到用Stack去解决String题？

  • Stack? - 用iterative遍历，看到某些element，不能马上用，要先存下来，以后再用。
  • 需要用就近原则去解决问题的时候。remove k adjacent duplicates，decode string with nested brackets
  • strStack + countStack 同压同弹 ⇒ strStack is to save char/substring to repeat, countStack is to save how many times we need to repeat the respective char

• Good Code-Writing Examples

  • 怎么去 convert digits in a String format？i.e. String “18” ⇒ int 18?
  • Remove empty space at the end?
  • String的corner case都有什么？

• Two Pointers 模版

  while (fast < len) {
    if keeping, copy fast to slow, slow++ fast++
  	else (discarding) fast++ 
  }
  return new String(charArray, 0, slow)
  
  // while loop里考虑在不同情况下，fast怎么动，slow怎么动
  // fast和slow的初始值可以节省edge case，让代码简介. (slow = 1 and fast = 1 at Remove All Adjacent Duplicates In String)
  // when discarding, we can set some additional condition (i.e. while loop) to remove a block of unnecessary elements more efficiently.
  // 遍历方向： 没必要一定要让fast从左到右的移动。方便时也可以从右到左 - String Replacement (replace longer)
  

• Other Tips </aside>

<aside> 📌 易错点

• 指针移动时，一定要确保要动， 避免死循环。而且要动的步数对。写完自己过一遍指针。
  • 移动步数跟string长度一样，或者跟index的差距一样的时候一定要算好什么时候要 +1 or -1
• 每次在while loop里面移动指针时，确保变量不会越界。 i.e. String Replacement里fast 和 lastIndex 变量 </aside>

String APIs

new String(char[] value, int offset, int count)  //(charArr, startIndex, subArrLen)
str.substring(int beginIndex, int endIndex)     // including startIndex, excluding endIndex
a

sb.length()     // StringBuilder‘s size
sb.charAt(i)    // not sb.get(i)
sb.delete(int startingIndex, int lengthToDelete)
sb.deleteCharAt(i)
sb.append()
sb.toString()
sb.reverse()

Character.isDigit(char ch)
Character.isAlphabet(char ch)

<aside> 🌵 Table of Contents

</aside>

Remove

Date: July 14, 2023

Problem: Remove Certain Characters

Date: July 14, 2023

Problem: Remove Space

Date: July 14, 2023

Problem: Remove All Adjacent Duplicates In String

Date: July 14, 2023

Problem: Remove K Adjacent Duplicates in String II (巧妙 - charDeque + countDeque)