GitHub上的代码链接
/**
* @Author: DaleyZou
* @Description: 重建二叉树
* 输入某二叉树的前序遍历和中序遍历的结果,请重建出该二叉树。
* 假设输入的前序遍历和中序遍历的结果中都不含重复的数字。
* 例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6},则重建二叉树并返回。
* @Date: Created in 7:58 2019/1/29
* @Modified By:
*/
public class ConstructBinaryTree_4 {
public static class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) { val = x; }
}
/**
* 缓存中序遍历数组每个值对应的索引
*/
private Map<Integer, Integer> indexForInOrders = new HashMap<>();
public TreeNode reConstructBinaryTree(int [] pre, int [] in) {
for (int i = 0; i < in.length; i++){
indexForInOrders.put(in[i], i);
}
return reConstructBinaryTree(pre, 0, pre.length - 1, 0);
}
public TreeNode reConstructBinaryTree(int [] pre, int preL, int preR, int inL){
if (preL > preR){
return null;
}
TreeNode root = new TreeNode(pre[preL]);
int inIndex = indexForInOrders.get(root.val);
int leftTreeSize = inIndex - inL;
root.left = reConstructBinaryTree(pre, preL + 1, preL + leftTreeSize, inL);
root.right = reConstructBinaryTree(pre, preL + leftTreeSize + 1, preR, inL + leftTreeSize + 1);
return root;
}
public static void main(String[] args){
int[] pre = new int[]{1,2,4,7,3,5,6,8};
int[] in = new int []{4,7,2,1,5,3,8,6};
ConstructBinaryTree_4 constructBinaryTree = new ConstructBinaryTree_4();
TreeNode treeNode = constructBinaryTree.reConstructBinaryTree(pre, in);
System.out.println(treeNode.val);
}
}