原地址:
https://www.cnblogs.com/xiaohutu/p/10504586.html
a star 算法
https://www.baidu.com/s?wd=a%20star%20%E7%AE%97%E6%B3%95&rsv_spt=1&rsv_iqid=0xc13fdc9800054ecc&issp=1&f=8&rsv_bp=0&rsv_idx=2&ie=utf-8&tn=baiduhome_pg&rsv_enter=1&rsv_sug3=10&rsv_sug1=10&rsv_sug7=101&rsv_t=0961cnU7eeWH27XjxkLDlkq9C%2F7w23lrouCfGDjC5VpWGjiy2ZXaju4gOjbh6c1udoJQ