求次短路徑……修改 Dijkstra，不只記錄到各點的最短距離（d[i]），還記錄次短距離（sd[i]）
實作上有幾點要注意（ 不確定這樣想對不對… ）：
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| (defpackage :pacman | |
| (:use :cl)) | |
| (in-package :pacman) | |
| ;;; The charms/ll library contains all of the FFI bindings to Ncurses. | |
| (ql:quickload :cl-charms) | |
| ;;; Here are all of the functions I'll be using from Ncurses. | |
| (import '( |
