算法练习之从String.indexOf的模拟实现开始

String.indexOf的模拟实现，没想象中有多么高深的查找算法，就是最普通的遍历查找

思路：先找到第一个相同的字符，然后依次比较后面的字符，若都相等则表示查找成功

 
  public int firstIndexOf(String str, String pattern) { 
    for (int i = 0; i < (str.length() - pattern.length()); i++) { 
      int j = 0; 
      while (j < pattern.length()) { 
 if (str.charAt(i + j) != pattern.charAt(j)) break; 
 j++; 
      } 
      if(j==pattern.length()) return i; 
    } 
    return -1; 
  } 
 
   
  public int lastIndexOf(String str, String pattern) { 
    for (int i = str.length() - pattern.length(); i >= 0; i--) { 
      int j = 0; 
      while (j < pattern.length()) { 
 if (str.charAt(i + j) != pattern.charAt(j)) break; 
 j++; 
      } 
      if (j == pattern.length()) return i; 
    } 
    return -1; 
  } 
 
   
  public List indexOf(String str, String pattern) { 
    List indexs = new ArrayList(); 
    for (int i = 0; i < (str.length() - pattern.length()); i++) { 
      int j = 0; 
      while (j < pattern.length()) { 
 if (str.charAt(i + j) != pattern.charAt(j)) break; 
 j++; 
      } 
      if (j == pattern.length()) indexs.add(i); 
    } 
    return indexs; 
  } 

同样更常用的String.contains方法实际上就是调用的String.indexOf实现

 
  public boolean contains(String str, String pattern) { 
    return firstIndexOf(str, pattern) != -1; 
  }