P143、面试题25：二叉树中和为某一值的路径

题目：输入一棵二叉树和一个整数，打印出二叉树中结点值的和为输入整数的所有路径。从树的根结点开始往下一直到叶结点所经过的结点形成一条路径。二叉树结点的定义如下：
struct BinaryTreeNode{
       int      m_nValue;
       BinaryTreeNode*      m_pLeft;
       BinaryTreeNode*      m_pRight;
}

测试用例：

1）功能测试（二叉树有一条、多条符合条件的路径，二叉树中没有符合条件的路径）；

2）特殊输入测试（指向二叉树根结点的指针为null指针）。

代码实现：

package com.yyq;
import java.util.Iterator;
import java.util.Stack;
/**
 * Created by Administrator on 2015/9/20.
 */
public class PathInTree {
    public static void findPath_1(BinaryTreeNode pRoot, int expectedSum){
        if (pRoot == null)
            return;
        Stack<Integer> path = new Stack<Integer>();
        int currentSum = 0;
        findPath_2(pRoot, expectedSum, path, currentSum);
    }
    public static void findPath_2(BinaryTreeNode pRoot,int expectedSum,Stack<Integer> path,int currentSum){
        currentSum += pRoot.getM_nValue();
        path.push(pRoot.getM_nValue());
        //如果是叶结点，并且路径上结点的和等于输入的值
        //打印出这条路径
        boolean isLeaf = pRoot.getM_pLeft() == null && pRoot.getM_pRight() == null;
        if (currentSum == expectedSum && isLeaf){
            System.out.println("A path is found:");
            Iterator<Integer> it = path.iterator();
            while(it.hasNext()){
                System.out.print(it.next() + "\t");
            }
            System.out.println();
        }
        //如果不是叶结点，则遍历它的子节点
        if (pRoot.getM_pLeft()!= null){
            findPath_2(pRoot.getM_pLeft(), expectedSum, path, currentSum);
        }
        if (pRoot.getM_pRight()!=null){
            findPath_2(pRoot.getM_pRight(), expectedSum, path, currentSum);
        }
        // 在返回到父结点之前，在路径上删除当前结点，
        // 并在currentSum中减去当前结点的值
        currentSum -= pRoot.getM_nValue();
        path.pop();
    }
    // ====================测试代码====================
    public static void Test(String testName, BinaryTreeNode pRoot, int expectedSum)
    {
        if(testName != null)
            System.out.println(testName+" begins:");
        findPath_1(pRoot, expectedSum);
        System.out.println();
    }
    //        10
//         /      \
//        5        12
//       /\
//      4  7
// 有两条路径上的结点和为22
    public static void Test1()
    {
        BinaryTreeNode pNode10 = new BinaryTreeNode(10);
        BinaryTreeNode pNode5 = new BinaryTreeNode(5);
        BinaryTreeNode pNode12 = new BinaryTreeNode(12);
        BinaryTreeNode pNode4 = new BinaryTreeNode(4);
        BinaryTreeNode pNode7 = new BinaryTreeNode(7);
        pNode10.connectTreeNodes(pNode5, pNode12);
        pNode5.connectTreeNodes(pNode4, pNode7);
        System.out.println("Two paths should be found in Test1.");
        Test("Test1", pNode10, 22);
        pNode10 = null;
    }
    //        10
//         /      \
//        5        12
//       /\
//      4  7
// 没有路径上的结点和为15
    public static void Test2()
    {
        BinaryTreeNode pNode10 = new BinaryTreeNode(10);
        BinaryTreeNode pNode5 = new BinaryTreeNode(5);
        BinaryTreeNode pNode12 = new BinaryTreeNode(12);
        BinaryTreeNode pNode4 = new BinaryTreeNode(4);
        BinaryTreeNode pNode7 = new BinaryTreeNode(7);
        pNode10.connectTreeNodes(pNode5, pNode12);
        pNode5.connectTreeNodes(pNode4, pNode7);
        System.out.println("No paths should be found in Test2.");
        Test("Test2", pNode10, 15);
        pNode10 =null;
    }
    //            5
//              /
//             4
//            /
//           3
//          /
//         2
//        /
//       1
// 有一条路径上面的结点和为15
    public static void Test3()
    {
        BinaryTreeNode pNode5 = new BinaryTreeNode(5);
        BinaryTreeNode pNode4 = new BinaryTreeNode(4);
        BinaryTreeNode pNode3 = new BinaryTreeNode(3);
        BinaryTreeNode pNode2 = new BinaryTreeNode(2);
        BinaryTreeNode pNode1 = new BinaryTreeNode(1);
        pNode5.connectTreeNodes(pNode4, null);
        pNode4.connectTreeNodes(pNode3, null);
        pNode3.connectTreeNodes(pNode2, null);
        pNode2.connectTreeNodes(pNode1, null);
        System.out.println("One path should be found in Test3.");
        Test("Test3", pNode5, 15);
        pNode5 = null;
    }
    // 1
//  \
//   2
//    \
//     3
//      \
//       4
//        \
//         5
// 没有路径上面的结点和为16
    public static void Test4()
    {
        BinaryTreeNode pNode1 = new BinaryTreeNode(1);
        BinaryTreeNode pNode2 = new BinaryTreeNode(2);
        BinaryTreeNode pNode3 = new BinaryTreeNode(3);
        BinaryTreeNode pNode4 = new BinaryTreeNode(4);
        BinaryTreeNode pNode5 = new BinaryTreeNode(5);
        pNode1.connectTreeNodes(null, pNode2);
        pNode2.connectTreeNodes(null, pNode3);
        pNode3.connectTreeNodes(null, pNode4);
        pNode4.connectTreeNodes(null, pNode5);
        System.out.println("No paths should be found in Test4.");
        Test("Test4", pNode1, 16);
        pNode1 = null;
    }
    // 树中只有1个结点
    public static void Test5()
    {
        BinaryTreeNode pNode1 = new BinaryTreeNode(1);
        System.out.println("One path should be found in Test5.");
        Test("Test5", pNode1, 1);
        pNode1 = null;
    }
    // 树中没有结点
    public static void Test6()
    {
        System.out.println("No paths should be found in Test6.");
        Test("Test6", null, 0);
    }
    public static void main(String[] args)
    {
        Test1();
        Test2();
        Test3();
        Test4();
        Test5();
        Test6();
    }
}

 

结果输出：

Two paths should be found in Test1.

Test1 begins:

A path is found:

10 5 7

A path is found:

10 12

 

No paths should be found in Test2.

Test2 begins:

 

One path should be found in Test3.

Test3 begins:

A path is found:

5 4 3 2 1

 

No paths should be found in Test4.

Test4 begins:

 

One path should be found in Test5.

Test5 begins:

A path is found:

1

 

No paths should be found in Test6.

Test6 begins: