我无法返回深度优先搜索

Question

我正在研究一种在六边形网格中找到路径的算法。为此，我使用深度为3的深度优先搜索。它在找到正确路径的意义上起作用。唯一的问题是它不会返回它。而是返回一个空集。

public Set findPath(Game game, Point origin, Point destination, Set<Point> hasVisited, int depth) throws Exception {
    if (origin.equals(destination)){
        System.out.println("Return from goal requirements: " + hasVisited);
        return hasVisited;
    }

    if (!origin.equals(destination)){
        if (depth != 0) {
            for (Point emptyNeighbor : getEmptyNeighbors(game, origin)) {
                if (!hasVisited.contains(emptyNeighbor)) {
                    if (!game.isHiveBrokenAfterPush(origin, emptyNeighbor)) {
                        hasVisited.add(emptyNeighbor);
                        game.push(origin.x, origin.y, emptyNeighbor.x, emptyNeighbor.y);

                        findPath(game, emptyNeighbor, destination, actualOrigin, hasVisited, depth - 1);

                        hasVisited.remove(emptyNeighbor);
                        game.push(emptyNeighbor.x, emptyNeighbor.y, origin.x, origin.y);
                    }
                }
            }
        }
    }

    System.out.println("Return from end of function: " + hasVisited);
    return hasVisited;
}

加载If语句后，它将节点添加到hasVisited并将块推向该方向。然后，它调用自身以继续在树的分支上。它删除hasVisited节点形式，如果无法解决，则取消推送。

现在发生的事情是，最终的回报似乎来自该函数的和。这些是它打印的最后几行：

Return from goal requirements: [java.awt.Point[x=-1,y=0], java.awt.Point[x=-2,y=1], java.awt.Point[x=-2,y=2]]
Return from end of function: [java.awt.Point[x=-1,y=0], java.awt.Point[x=-2,y=1]]
Return from end of function: [java.awt.Point[x=-1,y=0]]
Return from end of function: []
[]

上一组坐标应该返回。但您会看到它返回一个空集。

我试图返回findPath而不是仅仅执行它。这样做只会做一个分支。它不会取消无效的动作。我在代码中看不到问题，希望大家能帮帮我。干杯！

Answer 1

如果只有一种解决方案，请立即返回。递归将一个元素添加到集合中，递归调用并撤消添加。这将改变设置，即结果。当收集多个结果时，将复制该结果。

public boolean findPath(Game game, Point origin, Point destination, Set<Point> hasVisited,
            int depth) throws Exception {
    if (origin.equals(destination)){
        System.out.println("Return from goal requirements: " + hasVisited);
        return true;
    }

    if (depth != 0) {
        for (Point emptyNeighbor : getEmptyNeighbors(game, origin)) {
            if (!hasVisited.contains(emptyNeighbor)) {
                if (!game.isHiveBrokenAfterPush(origin, emptyNeighbor)) {
                    hasVisited.add(emptyNeighbor);
                    game.push(origin.x, origin.y, emptyNeighbor.x, emptyNeighbor.y);
                    boolean found = findPath(game, emptyNeighbor,
                            destination, actualOrigin, hasVisited, depth - 1);
                    if (found) {
                        return true;
                    }

                    hasVisited.remove(emptyNeighbor);
                    game.push(emptyNeighbor.x, emptyNeighbor.y, origin.x, origin.y);
                }
            }
        }
    }

    System.out.println("Not found");
    return false;
}