class PathInfo //数据存储结构
{
String from;
String to;
int distance;
boolean skip; // used in backtracking
PathInfo(String f, String t, int d)
{
from = f;
to = t;
distance = d;
skip = false;
}
}
public class Depth
{
final int MAX = 100;
PathInfo paths[] = new PathInfo[MAX];
int pathCount = 0;
Stack<PathInfo> goInfo = new Stack<PathInfo>();
public static void main(String args[])
{
String from = "", to = "";
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
try
{
System.out.print("From? ");
from = br.readLine();
System.out.print("To? ");
to = br.readLine();
} catch (IOException exc)
{
System.out.println("Error on input.");
}
Depth depth = new Depth();
depth.setup();
depth.isOK(from, to);
depth.route();
}
void isOK(String from, String to)// 将可行的路径压栈
{
int dist = match(from, to);
if (dist != 0) // 一站到达
{
goInfo.push(new PathInfo(from, to, dist));
return;
}
PathInfo pinfo = findFrom(from);
if (pinfo != null)
{
goInfo.push(new PathInfo(from, to, pinfo.distance));
isOK(pinfo.to, to); // 直到有“一站到达”
} else if (goInfo.size() > 0)
{
pinfo = (PathInfo) goInfo.pop();// 死路一条
isOK(pinfo.from, pinfo.to);// 回头再走,成立即可
}
}
void route()
{
if (goInfo.size() == 0)
return;
int num = goInfo.size();
Stack<PathInfo> backInfo = new Stack();
for (int i = 0; i < num; i++)
backInfo.push(goInfo.pop());// 倒出来,再pop,就是正序了
int dist = 0;
PathInfo pinfo = null;
for (int i = 0; i < num; i++)
{
pinfo = (PathInfo) backInfo.pop();
System.out.print(pinfo.from + " to ");
dist += pinfo.distance;
}
System.out.println(pinfo.to);
System.out.println("Distance is " + dist);
}
// 看能不能直到,能的话,就返回权重,不能返回0
int match(String from, String to)
{
for (int i = pathCount - 1; i > -1; i--)
{
if (paths[i].from.equals(from) && paths[i].to.equals(to) && !paths[i].skip)
{
paths[i].skip = true; // prevent reuse
return paths[i].distance;
}
}
return 0;
}
// Put flights into the database.
void addFlight(String from, String to, int dist)
{
if (pathCount < MAX)
{
paths[pathCount] = new PathInfo(from, to, dist);
pathCount++;
} else
System.out.println("Flight database full.\n");
}
// Given from, find any connection.
// 找到一个起点为from的,并再new一份出来,这段路的条件是未走过。
PathInfo findFrom(String from)
{
for (int i = 0; i < pathCount; i++)
{
if (paths[i].from.equals(from) && !paths[i].skip)
{
PathInfo pinfo = new PathInfo(paths[i].from, paths[i].to, paths[i].distance);
paths[i].skip = true; // prevent reuse
return pinfo;
}
}
return null;
}
// Initialize the path database.
// 地图是有限的,每个点周边相邻的点,两两成一直线,且是有方向性的
// 查找的时候,数据的分布,会影响结果
public void setup()
{
databaseGen();
}
private void databaseGen()
{
addFlight("A", "B", 500);
addFlight("A", "D", 900);
addFlight("A", "C", 1800);
addFlight("A", "J", 700);
addFlight("J", "K", 300);
addFlight("B", "A", 1700);
addFlight("B", "F", 1700);
// addFlight("B", "H", 600);
addFlight("B", "D", 500);
addFlight("C", "G", 1000);
addFlight("C", "E", 1000);
addFlight("C", "H", 1000);
addFlight("D", "C", 1000);
addFlight("E", "H", 1500);
}
private void databaseGood() // 最理想的情况,A to B
{
addFlight("A", "B", 500);
}
private void databaseLong()// 不理想的数据分布, A to J
{
addFlight("A", "B", 1500);
addFlight("A", "I", 1500);
addFlight("I", "J", 1500);
addFlight("B", "C", 1500);
addFlight("B", "A", 1500);
addFlight("C", "D", 1500);
addFlight("C", "B", 1500);
addFlight("D", "C", 1500);
}
private void databaseLong2()// 不理想的数据分布, A to J
{
addFlight("A", "B", 1500);
addFlight("A", "I", 1500);
addFlight("I", "J", 1500);
addFlight("B", "A", 1500);// --
addFlight("B", "C", 1500);// --
addFlight("C", "B", 1500);// --
addFlight("C", "D", 1500);// --
addFlight("D", "C", 1500);
}
}
数据存储特征:
一、上面的地图数据结构,映射为二维表。
二、起点集合性(就是from集在一起)
三、from按A->Z,to 是A->Z 或 Z->A
数据查找特征:
一、深度优先,如果是二维表的角度来说是,从左到右,从上至下。
查找优化:
一、将from分成块,那就能加快from的查找;
二、较短路径:
1、先得到起点与终点的直线距离X值,再由X经某种公式得到K值。
2、查找时判断时,排除权值大于K的
飞机就是典型、理想的点对点模型,
汽车的GPS导航就更复杂了,有路径最短、最省钱、最快速的