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1我们先来模拟创建一个二叉树
public class TestBinaryTreee {static class TreeNode{public char val;public TreeNode left;public TreeNode right;public TreeNode(char val) {this.val = val;}}public TreeNode creatTree(){TreeNode A = new TreeNode('A');TreeNode B = new TreeNode('B');TreeNode C = new TreeNode('C');TreeNode D = new TreeNode('D');TreeNode E = new TreeNode('E');TreeNode F = new TreeNode('F');TreeNode G = new TreeNode('G');TreeNode H = new TreeNode('H');A.left = B;A.right = C;B.left = D;B.right = E;C.left = F;C.right = G;E.right = H;return A;//就是根节点}
}2分别实现它的前中后序遍历
1前序遍历
// 前序遍历void preOrder(TreeNode root){if (root == null){return;}System.out.print(root.val+" ");//递归遍历左子树preOrder(root.left);//第归遍历右子树preOrder(root.right );} TestBinaryTreee testBinaryTreee = new TestBinaryTreee();testBinaryTreee.creatTree();TestBinaryTreee.TreeNode root = testBinaryTreee.creatTree();testBinaryTreee.preOrder(root);System.out.println();
2中序遍历
// 中序遍历void inOrder(TreeNode root){if (root == null){return;}inOrder(root.left);System.out.print(root.val+" ");inOrder(root.right);} testBinaryTreee.inOrder(root);System.out.println();
3后序遍历
// 后序遍历void postOrder(TreeNode root){if (root == null){return;}inOrder(root.left);inOrder(root.right);System.out.print(root.val+" ");}testBinaryTreee.postOrder(root);System.out.println();
3 获取树中节点的个数
//求有多少个节点
1:public int size(TreeNode root){if (root == null){return 0;}int ret = size(root.left)+size(root.right)+1;return ret;}
2:public static int nodeSize;public void size2(TreeNode root){if (root == null){return ;}nodeSize++;size2(root.left);size2(root.right);} System.out.println(testBinaryTreee.size(root));testBinaryTreee.size2(root);System.out.println(TestBinaryTreee.nodeSize);
4获取叶子节点的个数
//求叶子结点个数
1:public int getLeafNodeCount(TreeNode root){if (root == null){return 0;}if(root.left == null && root.right ==null){return 1;}return getLeafNodeCount(root.left)+getLeafNodeCount(root.right);}
2:public int leafSize;public void getLeafNodeCount2(TreeNode root){if (root == null){return ;}if(root.left == null && root.right ==null){leafSize++;}getLeafNodeCount2(root.left);getLeafNodeCount2(root.right);} System.out.println(testBinaryTreee.getLeafNodeCount(root));testBinaryTreee.getLeafNodeCount2(root);System.out.println(testBinaryTreee.leafSize);
5 获取第K层节点的个数
//获取第k层节点个数public int getKLevelNodeCount(TreeNode root,int k){if(root == null){return 0;}if (k==1){return 1;}return getKLevelNodeCount(root.left,k-1)+getKLevelNodeCount(root.right,k-1);}System.out.println(testBinaryTreee.getKLevelNodeCount(root, 3));
6获取二叉树的高度
//获取二叉树高度public int getHeight(TreeNode root){if(root == null){return 0;}int leftHeight = getHeight(root.left);int rightHeight = getHeight(root.right);return leftHeight > rightHeight ?leftHeight+1 : rightHeight+1;}int height = testBinaryTreee.getHeight(root);System.out.println(height);
7检测值为value的元素是否存在
// 检测值为val的元素是否存在public TreeNode find(TreeNode root,char val){if(root == null){return null;}if (root.val == val ){return root;}TreeNode ret = find(root.left,val);if (ret != null){return ret;}ret = find(root.right,val);if (ret != null){return ret;}return null;}TestBinaryTreee.TreeNode retN = testBinaryTreee.find(root, 'E');System.out.println(retN.val);
