java(simple)warmup1

最新推荐文章于 2024-09-19 16:03:20 发布

原创最新推荐文章于 2024-09-19 16:03:20 发布 · 338 阅读

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本文介绍了三种基本的字符串操作方法：在字符串前添加特定字符但保留原有条件不变、交换字符串首尾字符位置以及根据特定条件选择性地提取字符串开头的字符。通过具体示例展示了这些操作的实现过程。

Given a string, return a new string where “not ” has been added to the front. However, if the string already begins with “not”, return the string unchanged. Note: use .equals() to compare 2 strings.

notString(“candy”) → “not candy”
notString(“x”) → “not x”
notString(“not bad”) → “not bad”
.equals() use to compare the string ;
== don’t use to compare the string

public String notString(String str) {
  if(str.length()<3) return "not "+str;
  else if((str.substring(0,3)).equals("not")) return str;
  else return "not " + str;
}

public String notString(String str) {
  if (str.length() >= 3 && str.substring(0, 3).equals("not")) {
    return str;
  }

  return "not " + str;
}

Given a string, return a new string where the first and last chars have been exchanged.

frontBack(“code”) → “eodc”
frontBack(“a”) → “a”
frontBack(“ab”) → “ba”
str.substring(k,k) for “”(null)

public String frontBack(String str) {

  int n= str.length()-1;
  if(n<=0) return str;
  else if(n==1) return str.substring(1)+str.substring(0,1);
  return str.substring(n)+str.substring(1,n)+str.substring(0,1);
}

public String frontBack(String str) {
  if (str.length() <= 1) return str;

  String mid = str.substring(1, str.length()-1);

  // last + mid + first
  return str.charAt(str.length()-1) + mid + str.charAt(0);
}

Given a string, return a string made of the first 2 chars (if present), however include first char only if it is ‘o’ and include the second only if it is ‘z’, so “ozymandias” yields “oz”.

startOz(“ozymandias”) → “oz”
startOz(“bzoo”) → “z”
startOz(“oxx”) → “o”
use .charAt()==”k”(true)
don’t use .charAt().equals()(wrong)

public String startOz(String str) {
  int n=str.length();
  if(n>1 && str.substring(0,1).equals("o") && str.substring(1,2).equals("z")) return "oz";
  else if(n>0 && str.substring(0,1).equals("o")) return "o";
  else if(n>1 && str.substring(1,2).equals("z") ) return "z";
  else return "";

Solution:
public String startOz(String str) {
  String result = "";

  if (str.length() >= 1 && str.charAt(0)=='o') {
    result = result + str.charAt(0);
  }

  if (str.length() >= 2 && str.charAt(1)=='z') {
    result = result + str.charAt(1);
  }

  return result;
}