fix: a* in docs
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docs/A*.md
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docs/A*.md
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1. **可接受性(Admissibility)**:
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1. **可接受性(Admissibility)**:
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- 一个启发式函数是可接受的,如果它从不高估从节点到目标节点的实际最小成本。
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- 一个启发式函数是可接受的,如果它从不高估从节点到目标节点的实际最小成本。
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- 数学定义:对于所有节点 \(n\),启发式函数 \(h(n)\) 必须满足 \(h(n) \leq h^*(n)\),其中 \(h^*(n)\) 是从节点 \(n\) 到目标节点的实际成本。
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- 数学定义:对于所有节点 $n$,启发式函数 $h(n)$ 必须满足 $h(n) \leq h^*(n)$,其中 $h^*(n)$ 是从节点 $n$ 到目标节点的实际成本。
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2. **一致性(Consistency)**:
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2. **一致性(Consistency)**:
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- 一致性的启发式函数也称为单调性启发式函数。如果对于所有节点 \(n\) 和其每个子节点 \(m\),启发式函数 \(h\) 满足 \(h(n) \leq c(n, m) + h(m)\),其中 \(c(n, m)\) 是从节点 \(n\) 到节点 \(m\) 的实际成本。
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- 一致性的启发式函数也称为单调性启发式函数。如果对于所有节点 $n$ 和其每个子节点 $m$,启发式函数 $h$ 满足 $h(n) \leq c(n, m) + h(m)$,其中 $c(n, m)$ 是从节点 $n$ 到节点 $m$ 的实际成本。
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- 数学定义:\(h(n) \leq c(n, m) + h(m)\)。
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- 数学定义:$h(n) \leq c(n, m) + h(m)$。
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### 启发式函数的示例
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### 启发式函数的示例
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1. **曼哈顿距离(Manhattan Distance)**:
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1. **曼哈顿距离(Manhattan Distance)**:
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- 在网格路径规划中,曼哈顿距离是两个点之间沿轴线方向的总距离。
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- 在网格路径规划中,曼哈顿距离是两个点之间沿轴线方向的总距离。
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- 公式:\(h(n) = |x_1 - x_2| + |y_1 - y_2|\)。
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- 公式:$h(n) = |x_1 - x_2| + |y_1 - y_2|$。
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2. **欧几里得距离(Euclidean Distance)**:
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2. **欧几里得距离(Euclidean Distance)**:
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- 欧几里得距离是两点之间的直线距离。
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- 欧几里得距离是两点之间的直线距离。
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- 公式:\(h(n) = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2}\)。
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- 公式:$h(n) = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2}$。
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## A*搜索算法
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## A*搜索算法
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### 什么是A*搜索?
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### 什么是A*搜索?
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A*搜索是一种图搜索算法,它结合了Dijkstra算法和贪婪最佳优先搜索的优点。A*搜索使用启发式函数来引导搜索方向,从而找到从起始点到目标点的最优路径。
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A\*搜索是一种图搜索算法,它结合了Dijkstra算法和贪婪最佳优先搜索的优点。A*搜索使用启发式函数来引导搜索方向,从而找到从起始点到目标点的最优路径。
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### A*搜索的工作原理
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### A*搜索的工作原理
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@ -48,15 +48,14 @@ A*搜索是一种图搜索算法,它结合了Dijkstra算法和贪婪最佳优
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- 重复上述步骤,直到找到目标节点或优先队列为空。
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- 重复上述步骤,直到找到目标节点或优先队列为空。
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3. **代价函数**:
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3. **代价函数**:
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- A*搜索使用一个代价函数 \(f(n) = g(n) + h(n)\) 来评估每个节点的优先级。
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- A*搜索使用一个代价函数 $f(n) = g(n) + h(n)$ 来评估每个节点的优先级。
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- 其中,\(g(n)\) 是从起始节点到节点 \(n\) 的实际代价,\(h(n)\) 是从节点 \(n\) 到目标节点的启发式估计代价。
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- 其中,$g(n)$ 是从起始节点到节点 $n$ 的实际代价,$h(n)$ 是从节点 $n$ 到目标节点的启发式估计代价。
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### A*搜索的伪代码
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### A*搜索的伪代码
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```pseudo
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```pseudo
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function A*(start, goal)
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function A*(start, goal)
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openSet := {start}
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openSet := {start}
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cameFrom := empty map
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gScore := map with default value of Infinity
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gScore := map with default value of Infinity
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gScore[start] := 0
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gScore[start] := 0
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while openSet is not empty
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while openSet is not empty
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current := node in openSet with lowest fScore[current]
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current := node in openSet with lowest fScore[current]
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if current == goal
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if current == goal
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return reconstruct_path(cameFrom, current)
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return success
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openSet.remove(current)
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openSet.remove(current)
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for each neighbor of current
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for each neighbor of current
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tentative_gScore := gScore[current] + d(current, neighbor)
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tentative_gScore := gScore[current] + d(current, neighbor)
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if tentative_gScore < gScore[neighbor]
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if tentative_gScore < gScore[neighbor]
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cameFrom[neighbor] := current
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gScore[neighbor] := tentative_gScore
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gScore[neighbor] := tentative_gScore
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fScore[neighbor] := gScore[neighbor] + heuristic(neighbor, goal)
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fScore[neighbor] := gScore[neighbor] + heuristic(neighbor, goal)
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if neighbor not in openSet
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if neighbor not in openSet
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openSet.add(neighbor)
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openSet.add(neighbor)
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return failure
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return failure
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function reconstruct_path(cameFrom, current)
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total_path := {current}
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while current in cameFrom
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current := cameFrom[current]
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total_path.prepend(current)
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return total_path
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```
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```
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### A*搜索的应用
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### A*搜索的应用
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@ -43,7 +43,7 @@ Minimax 是一种用于两人对弈游戏的决策算法,如国际象棋、井
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```
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```
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X | O | X X | O | X X | O | X
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X | O | X X | O | X X | O | X
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----------- ----------- -----------
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----------- ----------- -----------
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O | X | X O | X | O | X |
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O | X | X O | X | O | X |
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----------- ----------- -----------
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----------- ----------- -----------
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| | O X | | O X | | O
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| | O X | | O X | | O
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```
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```
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@ -58,7 +58,7 @@ Minimax 是一种用于两人对弈游戏的决策算法,如国际象棋、井
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```
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```
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X | O | X X | O | X X | O | X
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X | O | X X | O | X X | O | X
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----------- ----------- -----------
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----------- ----------- -----------
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O | X | X O | X | O | X |
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O | X | X O | X | O | X |
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----------- ----------- -----------
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----------- ----------- -----------
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| | O X | | O X | | O
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| | O X | | O X | | O
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@ -107,6 +107,16 @@ function minimax(node, depth, maximizingPlayer)
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Alpha-Beta 剪枝是 Minimax 算法的一种优化。它通过剪枝那些不会影响最终决策的分支,减少需要评估的节点数量。
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Alpha-Beta 剪枝是 Minimax 算法的一种优化。它通过剪枝那些不会影响最终决策的分支,减少需要评估的节点数量。
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### Alpha-Beta 剪枝的基本思想
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Alpha-Beta 剪枝的主要思想是:在某些情况下,可以提前停止对某些节点的评估,因为这些节点不会影响最终的决策。
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- **Alpha 值**:当前节点在最大化玩家层面上可以得到的最高分数。
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- **Beta 值**:当前节点在最小化玩家层面上可以得到的最低分数。
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如果在搜索过程中发现一个节点的评估值无法改进当前的 Alpha 或 Beta 值,就可以停止对该节点的进一步搜索。
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### 带 Alpha-Beta 剪枝的伪代码
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### 带 Alpha-Beta 剪枝的伪代码
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```pseudo
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```pseudo
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@ -120,7 +130,7 @@ function alphabeta(node, depth, α, β, maximizingPlayer)
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eval = alphabeta(child, depth - 1, α, β, false)
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eval = alphabeta(child, depth - 1, α, β, false)
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maxEval = max(maxEval, eval)
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maxEval = max(maxEval, eval)
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α = max(α, eval)
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α = max(α, eval)
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if β <= α
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if β < α
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break
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break
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return maxEval
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return maxEval
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else
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else
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eval = alphabeta(child, depth - 1, α, β, true)
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eval = alphabeta(child, depth - 1, α, β, true)
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minEval = min(minEval, eval)
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minEval = min(minEval, eval)
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β = min(β, eval)
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β = min(β, eval)
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if β <= α
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if β < α
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break
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break
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return minEval
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return minEval
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```
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```
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