剑指offer 07 重建二叉树 Java

public class RebuildBinaryTree07_ {
    static class Node {
        int val;
        Node left;
        Node right;
        public Node(int val){
            this.val = val;
        }

        @Override
        public String toString() {
            return "Node{" +
                    "val=" + val +
                    ", left=" + left +
                    ", right=" + right +
                    '}';
        }
    }
    public static void main(String[] args) {
        int[] pre = {3, 9, 20, 15, 7};
        int[] in =  {9, 3, 15, 20, 7};
        Node root = rebuild(pre, in, 0, 4, 0, 4);
        System.out.println(root);
    }

    private static Node rebuild(int[] pre, int[] in, int prelo, int prehi, int inlo, int inhi) {
        if (prelo > prehi || inlo > inhi) {
            return null;
        }
        int i = inlo;
        for (; i <= inhi; i++) {
            if (in[i] == pre[prelo]) {
                break;
            }
        }
        Node root = new Node(pre[prelo]);
        root.left = rebuild(pre, in, prelo + 1, prelo + i, inlo, i - 1);
        root.right = rebuild(pre, in, prelo + i + 1, prehi, i + 1, inhi);
        return root;
    }
}

解释：需要注意递归时的始末下标