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SubTree.java
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package Chap3;
/**
* 输入两棵二叉树A，B，判断B是不是A的子结构。
* ps：我们约定空树不是任意一个树的子结构
*/
public class SubTree {
private class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
public boolean hasSubTree(TreeNode root1,TreeNode root2) {
boolean result = false;
if (root1 != null && root2 != null) {
// 根结点相同，紧接着判断子树结构一样不
if (root1.val == root2.val) {
result = doesTree1HaveTree2(root1, root2);
}
// 当前根结点不同，或者即使根结点相同子树结构不同，还需继续遍历，递归判断左右子树
if (!result) {
result = hasSubTree(root1.left, root2);
}
if (!result) {
result = hasSubTree(root1.right, root2);
}
}
return result;
}
private boolean doesTree1HaveTree2(TreeNode node1,TreeNode node2) {
// node2到达叶子结点的左右子结点了都还相等，说明是树1的子结构
if (node2 == null) {
return true;
}
// 如果node2没有到叶子结点的左右子结点，而node1先到了说明树2比树1还大，返回false
if (node1 == null) {
return false;
}
if (node1.val != node2.val) {
return false;
}
return doesTree1HaveTree2(node1.left, node2.left) && doesTree1HaveTree2(node1.right, node2.right);
}
}