面试题 25: 二叉树中和为某一值的路径

package week_5;

import java.util.ArrayList;

/**难度系数:***
* 剑指offer: 二叉树中和为某一个值的路径
* 方法: 熟悉二叉搜索树的概念,左子树所有结点小于根节点,右子树所有结点都大于根节点,左右子树仍是二叉搜索树,键值都不相等
* 测试用例: 递归
* @author dingding
* Date:2017-7-11 21:40
* Declaration: All Rights Reserved!
*/
public class No25 {

public static void main(String[] args) {
test1();
test2();
test3();
}

//solution
private static void findPath(BinaryTreeNode root,int expectedSum){
if (root == null) {
return;
}
ArrayList<Integer> paths = new ArrayList<>(); //存储路径
int currentSum = 0;
findPath(root, expectedSum,paths,currentSum);
}

private static void findPath(BinaryTreeNode root,int expectedSum,
ArrayList<Integer> paths,int currentSum){
currentSum +=root.value;
paths.add(root.value);

boolean isLeaf = (root.left == null && root.right == null);
if (currentSum == expectedSum && isLeaf) {
System.out.println("A path is found: ");
for (int path:paths){
System.out.print(" "+path);
}
System.out.println();
}

//如果不是叶子结点
if (root.left != null) {
findPath(root.left, expectedSum, paths, currentSum);
}
if (root.right != null) {
findPath(root.right, expectedSum, paths, currentSum);
}

//若当前已是叶子结点,移除当前节点
paths.remove(paths.size()-1);
}
/*====================测试用例================*/
private static void test1() {
BinaryTreeNode root = new BinaryTreeNode(10);
root.left = new BinaryTreeNode(5);
root.left.left = new BinaryTreeNode(4);
root.left.right = new BinaryTreeNode(7);
root.right = new BinaryTreeNode(12);

// 有两条路径上的结点和为22
System.out.println("findPath(root, 22);");
findPath(root, 22);
System.out.println();

// 没有路径上的结点和为15
System.out.println("findPath(root, 15);");
findPath(root, 15);
System.out.println();

// 有一条路径上的结点和为19
System.out.println("findPath(root, 19);");
findPath(root, 19);
System.out.println();
}

private static void test2() {
BinaryTreeNode root3 = new BinaryTreeNode(1);
root3.right = new BinaryTreeNode(2);
root3.right.right = new BinaryTreeNode(3);
root3.right.right.right = new BinaryTreeNode(4);
root3.right.right.right.right = new BinaryTreeNode(5);

// 有一条路径上面的结点和为15
System.out.println("findPath(root3, 15);");
findPath(root3, 15);
System.out.println();

// 没有路径上面的结点和为16
System.out.println("findPath(root3, 16);");
findPath(root3, 16);
System.out.println();

}

private static void test3() {
// 树中没有结点
System.out.println("findPath(null, 0);");
findPath(null, 0);
}

}

class BinaryTreeNode{
int value;
BinaryTreeNode left;
BinaryTreeNode right;

public BinaryTreeNode(int value){
this.value = value;
this.left = null;
this.right = null;
}
}