代码随想三刷二叉树篇1

本文主要是介绍代码随想三刷二叉树篇1，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

144. 二叉树的前序遍历

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<Integer> preorderTraversal(TreeNode root) {List<Integer> list = new ArrayList();pre(root,list);return list;}public void pre(TreeNode root,List<Integer> list){if(root==null){return;}list.add(root.val);pre(root.left,list);pre(root.right,list);}
}

145. 二叉树的后序遍历

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<Integer> postorderTraversal(TreeNode root) {List<Integer> list = new ArrayList();pos(root,list);return list;}public void pos(TreeNode root,List<Integer> list){if(root==null){return;}pos(root.left,list);pos(root.right,list);list.add(root.val);}
}

94. 二叉树的中序遍历

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<Integer> inorderTraversal(TreeNode root) {List<Integer> result = new ArrayList();pos(root,result);return result;}public void pos(TreeNode root,List<Integer> list){if(root==null){return;}pos(root.left,list);list.add(root.val);pos(root.right,list);}
}

102. 二叉树的层序遍历

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<List<Integer>> levelOrder(TreeNode root) {Deque<TreeNode> queue = new LinkedList();List<List<Integer>> result = new ArrayList();if(root==null){return result;}queue.addLast(root);while(!queue.isEmpty()){int size = queue.size();List<Integer> list = new ArrayList();for(int i = 0;i<size;i++){TreeNode temp = queue.removeFirst();list.add(temp.val);if(temp.left!=null){queue.addLast(temp.left);}if(temp.right!=null){queue.addLast(temp.right);}}result.add(list);}return result;}
}

107. 二叉树的层序遍历 II

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<List<Integer>> levelOrderBottom(TreeNode root) {List<List<Integer>> result = new ArrayList();Deque<TreeNode> queue = new LinkedList();if(root==null){return result;}queue.addLast(root);while(!queue.isEmpty()){int size = queue.size();List<Integer> list = new ArrayList();for(int i=0;i<size;i++){TreeNode t = queue.removeFirst();list.add(t.val);if(t.left!=null){queue.addLast(t.left);}if(t.right!=null){queue.addLast(t.right);}}result.add(0,list);}return result;}
}

199. 二叉树的右视图

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<Integer> rightSideView(TreeNode root) {List<Integer> result = new ArrayList();if(root==null){return result;}Deque<TreeNode> queue = new LinkedList();queue.addLast(root);while(!queue.isEmpty()){int size = queue.size();for(int i=0;i<size;i++){TreeNode t = queue.removeFirst();if(t.left!=null){queue.addLast(t.left);}if(t.right!=null){queue.addLast(t.right);}if(i==size-1){result.add(t.val);}}}return result;}
}

637. 二叉树的层平均值

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<Double> averageOfLevels(TreeNode root) {List<Double> result = new ArrayList();if(root==null){return result;}Deque<TreeNode> queue = new LinkedList();queue.addLast(root);while(!queue.isEmpty()){int size = queue.size();double sum = 0;for(int i=0;i<size;i++){TreeNode t = queue.removeFirst();sum += t.val;if(t.left!=null){queue.addLast(t.left);}if(t.right!=null){queue.addLast(t.right);}}result.add(sum/size);}return result;}
}

515. 在每个树行中找最大值

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<Integer> largestValues(TreeNode root) {List<Integer> result = new ArrayList();if(root==null){return result;}Deque<TreeNode> queue = new LinkedList();queue.addLast(root);while(!queue.isEmpty()){int size = queue.size();int num = Integer.MIN_VALUE;for(int i=0;i<size;i++){TreeNode t = queue.removeFirst();num = Math.max(num,t.val);if(t.left!=null){queue.addLast(t.left);}if(t.right!=null){queue.addLast(t.right);}}result.add(num);}return result;}
}

104. 二叉树的最大深度

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public int maxDepth(TreeNode root) {findDepth(root,1);return maxDepth;}int maxDepth = 0;public void findDepth(TreeNode root,int depth){if(root==null){return;}maxDepth = Math.max(maxDepth,depth);findDepth(root.left,depth+1);findDepth(root.right,depth+1);}
}

111. 二叉树的最小深度

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public int minDepth(TreeNode root) {if(root==null){return 0;}pre(root,1);return min;}   int min = Integer.MAX_VALUE;public void pre(TreeNode root,int depth){if(root==null){return;}if(root.left==null&&root.right==null){min = Math.min(min,depth);}pre(root.left,depth+1);pre(root.right,depth+1);}
}

226. 翻转二叉树

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/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public TreeNode invertTree(TreeNode root) {if(root==null||(root.left==null&&root.right==null)){return root;}TreeNode left= invertTree(root.left);TreeNode right= invertTree(root.right);root.left = right;root.right = left;return root;}
}

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