①直接求解，字典序輸出答案
HDU 1814 Peaceful Commission http://blog.csdn.net/a634771197/article/details/38585663
②二分枚舉答案，判有無解
HDU 1815 Building roads http://blog.csdn.net/a634771197/article/details/38585903
HDU 1816 Get Luffy Out * http://blog.csdn.net/a634771197/article/details/38586361