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C#-遍历二叉树,根据前序中序生成后序遍历

infgrad 2022-01-04 阅读 77

前序遍历和中序遍历,并且根据前序和中序遍历,生成后序遍历

class 题号75//遍历树
    {
        static void Main()
        {
            PostorderTraversal(1);
            Console.ReadKey();
            int[] pre = { 1, 2, 4, 8, 9, 5, 10, 3, 6, 7 };
            int[] mid = { 8, 4, 9, 2, 10, 5, 1, 6, 3, 7 };
            reConstructBinaryTree(pre, mid);
        }
        public static int[] data = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        #region
        //前序遍历
        public static void PreorderTraversal(int number)
        {
            // int number = 1;
            //当下标越界或者当前元素为'^'时此次递归分支终止
            if (number > data.Length || data[number - 1].Equals('^'))
            {
                return;
            }
            //Console.Write(data[number - 1] + " ");

            int leftChildNum = number * 2;
            PreorderTraversal(leftChildNum);

            int rightChildNum = number * 2 + 1;
            PreorderTraversal(rightChildNum);
        }
        #endregion
        #region
        //中序遍历
        public static void MiddleTraversal(int number)
        {
            //当下标越界或者当前元素为'^'时此次递归分支终止
            if (number > data.Length || data[number - 1].Equals('^'))
            {
                return;
            }
            int leftChildNum = number * 2;
            MiddleTraversal(leftChildNum);

            Console.Write(data[number - 1] + " ");

            int rightChildNum = number * 2 + 1;
            MiddleTraversal(rightChildNum);
        }
        #endregion
        #region
        //后续遍历
        public static void PostorderTraversal(int number)
        {
            //当下标越界或者当前元素为'^'时此次递归分支终止
            if (number > data.Length || data[number - 1].Equals('^'))
            {
                return;
            }
            int leftChildNum = number * 2;
            PostorderTraversal(leftChildNum);

            int rightChildNum = number * 2 + 1;
            PostorderTraversal(rightChildNum);

            Console.Write(data[number - 1] + " ");
        }
        #endregion
        #region
        //由前序遍历和中序遍历生成倒叙遍历
        public class TreeNode
        {
            public int val;       //当前节点的值
            public TreeNode left; 
            public TreeNode right;

            public TreeNode(int x)
            {
                val = x;
            }
        }
        public static void reConstructBinaryTree(int[] pre, int[] mid)
        {
            TreeNode newTree= getRootTreeNode(pre, 0, pre.Length - 1, mid, 0, mid.Length - 1);
            Console.ReadKey();

        }
        public static TreeNode getRootTreeNode(int[] pre, int preL,int preR, int[] mid, int inL, int inR)
        {
            if (preL > preR)
            {
                return null;
            }

            TreeNode node = new TreeNode(pre[preL]);

            for (int i = inL; i <= inR; ++i)
            {
                if (mid[i] == pre[preL]) 
                {
                    node.left = getRootTreeNode(pre, preL + 1, preL + i - inL, mid, inL, i - 1);
                    node.right = getRootTreeNode(pre, preL + i - inL + 1, preR, mid, i + 1, inR) ;
                    break;
                }
            }
            Console.WriteLine(node.val);
            return node;
        }
    #endregion
    }
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