二叉樹中值和為某一值的路徑：類似圖的深度優先遍歷

對於此類問題一直有點弱，多想幾次就OK了–主要是不熟悉，畢竟程式碼寫出來之後一看就明白，但是自己想的時候還是有點困難

    public class _Q25 {

    public void FindPathInTree(BinaryTreeNode<Integer> tree, int expectedSum){
        if(tree == null) return;

        Vector<BinaryTreeNode<Integer>> path = new Vector<>();
        int
 
 curSum = 0;

        FindAndPrintPath(tree, expectedSum, curSum, path);
    }

    private void FindAndPrintPath(BinaryTreeNode<Integer> tree, int expectedSum, 
            int curSum, Vector<BinaryTreeNode<Integer>> path){

        if(tree == null) return;

        curSum = curSum + tree.value
 
;
        path.add(tree);

        if(curSum == expectedSum && tree.leftChild == null && tree.rightChild == null){
            for(int i=0; i<path.size(); i++){
                System.out.print(path.get(i).value + " ");
            }
            System.out.println();
        }

        if
 
(tree.leftChild != null) FindAndPrintPath(tree.leftChild, expectedSum, curSum, path);
        if(tree.rightChild != null) FindAndPrintPath(tree.rightChild, expectedSum, curSum, path);

        path.remove(path.size() - 1); // 回溯
    }
    }

測試程式碼：

    public class _Q25Test extends TestCase {

    _Q25 printTreePath = new _Q25();

    public void test(){
        BinaryTreeNode<Integer> root = new BinaryTreeNode<>();
        BinaryTreeNode<Integer> node1 = new BinaryTreeNode<>();
        BinaryTreeNode<Integer> node2 = new BinaryTreeNode<>();
        BinaryTreeNode<Integer> node3 = new BinaryTreeNode<>();
        BinaryTreeNode<Integer> node4 = new BinaryTreeNode<>();

        root.value = 10;
        node1.value = 5;
        node2.value = 12;
        node3.value = 4;
        node4.value = 7;

        root.leftChild = node1;
        root.rightChild = node2;
        node1.leftChild = node3;
        node1.rightChild = node4;

        node2.leftChild = null; node2.rightChild = null;
        node3.leftChild = null; node3.rightChild = null;
        node4.leftChild = null; node4.rightChild = null;

        printTreePath.FindPathInTree(root, 22);
    }
    }