關於字符串的匹配問題;主字符串1 —> str1 = "xxxxI write themxxxxxxxx I write them here shows what I have been learning." ;
字符串2 —> str2= "I write them here shows what I have been learning.";
若字符串1包含字符串2,則返回開始出現的位置;否則返回-1;
參考來源：https://blog.csdn.net/MrTumnus/article/details/121679134