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分享a*算法是这样的吗？
黑色是障碍、黄色是找到的路径、绿色是访问过的节点，访问过这么多正常吗？还是我算法写错了？代码是DELPHI的就不贴了，那边没这边人多，大致就是
定义了这么一个结构
然后一个TNode的动态数组，没有排序，每次遍历这个列表找出F值最小的节点
现在都先不考虑效率问题了，访问过这么多点是正常的吗？这都接近穷举了！？地图大小要是上1000x1000根本就没法寻路了，20分钟能找出一条路都算快的了
参考文章http://www.cnblogs.com/technology/archive/2011/05/26/2058842.html
我一直对这句话没怎么理解
到底什么情况才有可能新的G值比旧的还小？
定义了这么一个结构
TNode = packed record
Father: Integer;//父节点
X: Integer;
Y: Integer;
G: Integer;
H: Integer;
F: Integer;
Status: Byte;//保存这个节点的状态 open还是close还是未访问，就没用两张表了
end;然后一个TNode的动态数组，没有排序，每次遍历这个列表找出F值最小的节点
现在都先不考虑效率问题了，访问过这么多点是正常的吗？这都接近穷举了！？地图大小要是上1000x1000根本就没法寻路了，20分钟能找出一条路都算快的了
参考文章http://www.cnblogs.com/technology/archive/2011/05/26/2058842.html
我一直对这句话没怎么理解
if (它已经在开启列表中)
if (用G值为参考检查新的路径是否更好, 更低的G值意味着更好的路径)
{
把这一格的父节点改成当前格, 并且重新计算这一格的 GF 值.
} 到底什么情况才有可能新的G值比旧的还小？
...全文
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shiter 2014-09-22
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路过学习，楼上厉害
fasmot 2014-09-21
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if (corner == walkable) {
// If not already on the open list, add it to the open list.
if (whichList[a][b] != onOpenList)
{
//Create a new open list item in the binary heap.
newOpenListItemID = newOpenListItemID + 1; //each new item has a unique ID #
m = numberOfOpenListItems+1;
openList[m] = newOpenListItemID;//place the new open list item (actually, its ID#) at the bottom of the heap
openX[newOpenListItemID] = a;
openY[newOpenListItemID] = b;//record the x and y coordinates of the new item
//Figure out its G cost
if (abs(a-parentXval) == 1 && abs(b-parentYval) == 1)
addedGCost = 14;//cost of going to diagonal squares
else
addedGCost = 10;//cost of going to non-diagonal squares
Gcost[a][b] = Gcost[parentXval][parentYval] + addedGCost;
//Figure out its H and F costs and parent
Hcost[openList[m]] = 10*(abs(a - targetX) + abs(b - targetY));
Fcost[openList[m]] = Gcost[a][b] + Hcost[openList[m]];
parentX[a][b] = parentXval ; parentY[a][b] = parentYval;
//Move the new open list item to the proper place in the binary heap.
//Starting at the bottom, successively compare to parent items,
//swapping as needed until the item finds its place in the heap
//or bubbles all the way to the top (if it has the lowest F cost).
while (m != 1) //While item hasn't bubbled to the top (m=1)
{
//Check if child's F cost is < parent's F cost. If so, swap them.
if (Fcost[openList[m]] <= Fcost[openList[m/2]])
{
temp = openList[m/2];
openList[m/2] = openList[m];
openList[m] = temp;
m = m/2;
}
else
break;
}
numberOfOpenListItems = numberOfOpenListItems+1;//add one to the number of items in the heap
//Change whichList to show that the new item is on the open list.
whichList[a][b] = onOpenList;
}
//8.If adjacent cell is already on the open list, check to see if this
// path to that cell from the starting location is a better one.
// If so, change the parent of the cell and its G and F costs.
else //If whichList(a,b) = onOpenList
{
//Figure out the G cost of this possible new path
if (abs(a-parentXval) == 1 && abs(b-parentYval) == 1)
addedGCost = 14;//cost of going to diagonal tiles
else
addedGCost = 10;//cost of going to non-diagonal tiles
tempGcost = Gcost[parentXval][parentYval] + addedGCost;
//If this path is shorter (G cost is lower) then change
//the parent cell, G cost and F cost.
if (tempGcost < Gcost[a][b]) //if G cost is less,
{
parentX[a][b] = parentXval; //change the square's parent
parentY[a][b] = parentYval;
Gcost[a][b] = tempGcost;//change the G cost
//Because changing the G cost also changes the F cost, if
//the item is on the open list we need to change the item's
//recorded F cost and its position on the open list to make
//sure that we maintain a properly ordered open list.
for (int x = 1; x <= numberOfOpenListItems; x++) //look for the item in the heap
{
if (openX[openList[x]] == a && openY[openList[x]] == b) //item found
{
Fcost[openList[x]] = Gcost[a][b] + Hcost[openList[x]];//change the F cost
//See if changing the F score bubbles the item up from it's current location in the heap
m = x;
while (m != 1) //While item hasn't bubbled to the top (m=1)
{
//Check if child is < parent. If so, swap them.
if (Fcost[openList[m]] < Fcost[openList[m/2]])
{
temp = openList[m/2];
openList[m/2] = openList[m];
openList[m] = temp;
m = m/2;
}
else
break;
}
break; //exit for x = loop
} //If openX(openList(x)) = a
} //For x = 1 To numberOfOpenListItems
}//If tempGcost < Gcost(a,b)
}//else If whichList(a,b) = onOpenList
}//If not cutting a corner
}//If not a wall/obstacle square.
}//If not already on the closed list
}//If not off the map
}//for (a = parentXval-1; a <= parentXval+1; a++){
}//for (b = parentYval-1; b <= parentYval+1; b++){
}//if (numberOfOpenListItems != 0)
//9.If open list is empty then there is no path.
else
{
path = nonexistent; break;
}
//If target is added to open list then path has been found.
if (whichList[targetX][targetY] == onOpenList)
{
path = found; break;
}
}
while (1);//Do until path is found or deemed nonexistent
//10.Save the path if it exists.
if (path == found)
{
//a.Working backwards from the target to the starting location by checking
// each cell's parent, figure out the length of the path.
pathX = targetX; pathY = targetY;
do
{
//Look up the parent of the current cell.
tempx = parentX[pathX][pathY];
pathY = parentY[pathX][pathY];
pathX = tempx;
//Figure out the path length
pathLength[pathfinderID] = pathLength[pathfinderID] + 1;
}
while (pathX != startX || pathY != startY);
//b.Resize the data bank to the right size in bytes
pathBank[pathfinderID] = (int*) realloc (pathBank[pathfinderID],
pathLength[pathfinderID]*8);
//c. Now copy the path information over to the databank. Since we are
// working backwards from the target to the start location, we copy
// the information to the data bank in reverse order. The result is
// a properly ordered set of path data, from the first step to the
// last.
pathX = targetX ; pathY = targetY;
cellPosition = pathLength[pathfinderID]*2;//start at the end
do
{
cellPosition = cellPosition - 2;//work backwards 2 integers
pathBank[pathfinderID] [cellPosition] = pathX;
pathBank[pathfinderID] [cellPosition+1] = pathY;
//d.Look up the parent of the current cell.
tempx = parentX[pathX][pathY];
pathY = parentY[pathX][pathY];
pathX = tempx;
//e.If we have reached the starting square, exit the loop.
}
while (pathX != startX || pathY != startY);
//11.Read the first path step into xPath/yPath arrays
ReadPath(pathfinderID,startingX,startingY,1);
}
return path;
//13.If there is no path to the selected target, set the pathfinder's
// xPath and yPath equal to its current location and return that the
// path is nonexistent.
noPath:
xPath[pathfinderID] = startingX;
yPath[pathfinderID] = startingY;
return nonexistent;
}
fasmot 2014-09-21
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/*
;===================================================================
;A* Pathfinder (Version 1.71a) by Patrick Lester. Used by permission.
;===================================================================
;Last updated 06/16/03 -- Visual C++ version
*/
//Declare constants
const mapWidth = 80, mapHeight = 60, tileSize = 10, numberPeople = 3;
int onClosedList = 10;
const notfinished = 0, notStarted = 0;// path-related constants
const found = 1, nonexistent = 2;
const walkable = 0, unwalkable = 1;// walkability array constants
//Create needed arrays
char walkability [mapWidth][mapHeight];
int openList[mapWidth*mapHeight+2]; //1 dimensional array holding ID# of open list items
int whichList[mapWidth+1][mapHeight+1]; //2 dimensional array used to record
// whether a cell is on the open list or on the closed list.
int openX[mapWidth*mapHeight+2]; //1d array stores the x location of an item on the open list
int openY[mapWidth*mapHeight+2]; //1d array stores the y location of an item on the open list
int parentX[mapWidth+1][mapHeight+1]; //2d array to store parent of each cell (x)
int parentY[mapWidth+1][mapHeight+1]; //2d array to store parent of each cell (y)
int Fcost[mapWidth*mapHeight+2]; //1d array to store F cost of a cell on the open list
int Gcost[mapWidth+1][mapHeight+1]; //2d array to store G cost for each cell.
int Hcost[mapWidth*mapHeight+2]; //1d array to store H cost of a cell on the open list
int pathLength[numberPeople+1]; //stores length of the found path for critter
int pathLocation[numberPeople+1]; //stores current position along the chosen path for critter
int* pathBank [numberPeople+1];
//Path reading variables
int pathStatus[numberPeople+1];
int xPath[numberPeople+1];
int yPath[numberPeople+1];
//-----------------------------------------------------------------------------
// Function Prototypes: where needed
//-----------------------------------------------------------------------------
void ReadPath(int pathfinderID,int currentX,int currentY, int pixelsPerFrame);
int ReadPathX(int pathfinderID,int pathLocation);
int ReadPathY(int pathfinderID,int pathLocation);
//-----------------------------------------------------------------------------
// Name: InitializePathfinder
// Desc: Allocates memory for the pathfinder.
//-----------------------------------------------------------------------------
void InitializePathfinder (void)
{
for (int x = 0; x < numberPeople+1; x++)
pathBank [x] = (int*) malloc(4);
}
//-----------------------------------------------------------------------------
// Name: EndPathfinder
// Desc: Frees memory used by the pathfinder.
//-----------------------------------------------------------------------------
void EndPathfinder (void)
{
for (int x = 0; x < numberPeople+1; x++)
{
free (pathBank [x]);
}
}
//-----------------------------------------------------------------------------
// Name: FindPath
// Desc: Finds a path using A*
//-----------------------------------------------------------------------------
int FindPath (int pathfinderID,int startingX, int startingY,
int targetX, int targetY)
{
int onOpenList=0, parentXval=0, parentYval=0,
a=0, b=0, m=0, u=0, v=0, temp=0, corner=0, numberOfOpenListItems=0,
addedGCost=0, tempGcost = 0, path = 0,
tempx, pathX, pathY, cellPosition,
newOpenListItemID=0;
//1. Convert location data (in pixels) to coordinates in the walkability array.
int startX = startingX/tileSize;
int startY = startingY/tileSize;
targetX = targetX/tileSize;
targetY = targetY/tileSize;
//2.Quick Path Checks: Under the some circumstances no path needs to
// be generated ...
// If starting location and target are in the same location...
if (startX == targetX && startY == targetY && pathLocation[pathfinderID] > 0)
return found;
if (startX == targetX && startY == targetY && pathLocation[pathfinderID] == 0)
return nonexistent;
// If target square is unwalkable, return that it's a nonexistent path.
if (walkability[targetX][targetY] == unwalkable)
goto noPath;
//3.Reset some variables that need to be cleared
if (onClosedList > 1000000) //reset whichList occasionally
{
for (int x = 0; x < mapWidth;x++) {
for (int y = 0; y < mapHeight;y++)
whichList [x][y] = 0;
}
onClosedList = 10;
}
onClosedList = onClosedList+2; //changing the values of onOpenList and onClosed list is faster than redimming whichList() array
onOpenList = onClosedList-1;
pathLength [pathfinderID] = notStarted;//i.e, = 0
pathLocation [pathfinderID] = notStarted;//i.e, = 0
Gcost[startX][startY] = 0; //reset starting square's G value to 0
//4.Add the starting location to the open list of squares to be checked.
numberOfOpenListItems = 1;
openList[1] = 1;//assign it as the top (and currently only) item in the open list, which is maintained as a binary heap (explained below)
openX[1] = startX ; openY[1] = startY;
//5.Do the following until a path is found or deemed nonexistent.
do
{
//6.If the open list is not empty, take the first cell off of the list.
// This is the lowest F cost cell on the open list.
if (numberOfOpenListItems != 0)
{
//7. Pop the first item off the open list.
parentXval = openX[openList[1]];
parentYval = openY[openList[1]]; //record cell coordinates of the item
whichList[parentXval][parentYval] = onClosedList;//add the item to the closed list
// Open List = Binary Heap: Delete this item from the open list, which
// is maintained as a binary heap. For more information on binary heaps, see:
// http://www.policyalmanac.org/games/binaryHeaps.htm
numberOfOpenListItems = numberOfOpenListItems - 1;//reduce number of open list items by 1
// Delete the top item in binary heap and reorder the heap, with the lowest F cost item rising to the top.
openList[1] = openList[numberOfOpenListItems+1];//move the last item in the heap up to slot #1
v = 1;
// Repeat the following until the new item in slot #1 sinks to its proper spot in the heap.
do
{
u = v;
if (2*u+1 <= numberOfOpenListItems) //if both children exist
{
//Check if the F cost of the parent is greater than each child.
//Select the lowest of the two children.
if (Fcost[openList[u]] >= Fcost[openList[2*u]])
v = 2*u;
if (Fcost[openList[v]] >= Fcost[openList[2*u+1]])
v = 2*u+1;
}
else
{
if (2*u <= numberOfOpenListItems) //if only child #1 exists
{
//Check if the F cost of the parent is greater than child #1
if (Fcost[openList[u]] >= Fcost[openList[2*u]])
v = 2*u;
}
}
if (u != v) //if parent's F is > one of its children, swap them
{
temp = openList[u];
openList[u] = openList[v];
openList[v] = temp;
}
else
break; //otherwise, exit loop
}
while (!KeyDown(27));//reorder the binary heap
//7.Check the adjacent squares. (Its "children" -- these path children
// are similar, conceptually, to the binary heap children mentioned
// above, but don't confuse them. They are different. Path children
// are portrayed in Demo 1 with grey pointers pointing toward
// their parents.) Add these adjacent child squares to the open list
// for later consideration if appropriate (see various if statements
// below).
for (b = parentYval-1; b <= parentYval+1; b++){
for (a = parentXval-1; a <= parentXval+1; a++){
// If not off the map (do this first to avoid array out-of-bounds errors)
if (a != -1 && b != -1 && a != mapWidth && b != mapHeight){
// If not already on the closed list (items on the closed list have
// already been considered and can now be ignored).
if (whichList[a][b] != onClosedList) {
// If not a wall/obstacle square.
if (walkability [a][b] != unwalkable) {
// Don't cut across corners
corner = walkable;
if (a == parentXval-1)
{
if (b == parentYval-1)
{
if (walkability[parentXval-1][parentYval] == unwalkable
|| walkability[parentXval][parentYval-1] == unwalkable) \
corner = unwalkable;
}
else if (b == parentYval+1)
{
if (walkability[parentXval][parentYval+1] == unwalkable
|| walkability[parentXval-1][parentYval] == unwalkable)
corner = unwalkable;
}
}
else if (a == parentXval+1)
{
if (b == parentYval-1)
{
if (walkability[parentXval][parentYval-1] == unwalkable
|| walkability[parentXval+1][parentYval] == unwalkable)
corner = unwalkable;
}
else if (b == parentYval+1)
{
if (walkability[parentXval+1][parentYval] == unwalkable
|| walkability[parentXval][parentYval+1] == unwalkable)
corner = unwalkable;
}
}
