發送短信 : Counting neighboring pairs in permutations

             ___      ______    _____     ______  
  ____      / _ \\   /_   _//  |  ___||  /_____// 
 |    \\   | / \ ||  `-| |,-   | ||__    `____ `  
 | [] ||   | \_/ ||    | ||    | ||__    /___//   
 |  __//    \___//     |_||    |_____||  `__ `    
 |_|`-`     `---`      `-`'    `-----`   /_//     
 `-`                                     `-`