day16 二叉树 part04

513 找树左下角的值 

import java.util.LinkedList;
import java.util.Queue;

import programmer.day13.TreeNode;

// @lc code=start
/**
 * 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 findBottomLeftValue(TreeNode root) {
    //     int ans = 0;
    //     Queue<TreeNode> queue = new LinkedList<>();
    //     queue.offer(root);
    //     while(!queue.isEmpty()){
    //         int size = queue.size();
    //         for(int i  = 0; i < size; i++){
    //             TreeNode node = queue.poll();
    //             if(i == 0){
    //                 ans = node.val;
    //             }
    //             if(node.left != null){
    //                 queue.offer(node.left);
    //             }
    //             if(node.right != null){
    //                 queue.offer(node.right);
    //             }
    //         }
    //     }
    //     return ans;
    // }


    private int DEEP = -1;
    private int ans;
    public int findBottomLeftValue(TreeNode root) {
        depth(root, 0);
        return ans;
    }

    private void depth(TreeNode node, int deep){
        if(node == null){
            return;
        }
        if(node.left == null && node.right == null && deep >DEEP){
            DEEP = deep;
            ans = node.val;
        }
        depth(node.left, deep + 1);
        depth(node.right, deep + 1);
    }
        

    
}

112. 路径总和

class Solution {
    public boolean hasPathSum(TreeNode root, int targetSum) {
        if(root == null){
            return false;
        }
        return backtracing(root, targetSum, 0);
    }

    private boolean backtracing(TreeNode node, int target, int current){
        current += node.val;
        if(node.left == null && node.right == null){
            return current == target;
        }
        if(node.left != null && backtracing(node.left, target, Integer.valueOf(current))){
            return true;
        }
        if(node.right != null && backtracing(node.right, target, Integer.valueOf(current))){
            return true;
        }
        return false;
    }
}

113. 路径总和ii

import java.util.ArrayList;
import java.util.List;

/**
 * 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 {
    List<List<Integer>> ans;
    List<Integer> path;
    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
        ans = new ArrayList<>();
        path = new ArrayList<>();
        if(root ==null){
            return ans;
        }
        int current = root.val;
        path.add(root.val);
        backtracing(root, targetSum, current, path);
        return ans;
    }

    private void backtracing(TreeNode node, int target, int current, List<Integer> path){
        if(node.left == null && node.right == null && current == target){
            ans.add(new ArrayList<>(path));
            return;
        }
        if(node.left != null){
            path.add(node.left.val);
            backtracing(node.left, target, current + node.left.val, path);
            path.remove(path.size() - 1);
        }
        if(node.right != null){
            path.add(node.right.val);
            backtracing(node.right, target, current + node.right.val, path);
            path.remove(path.size() - 1);
        }

    }
}

106.从中序与后序遍历序列构造二叉树

class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        // 闭开区间
        return buildTree(inorder, 0, inorder.length, postorder, 0, postorder.length);
        
    }

    private TreeNode buildTree(int[] inorder, int inStart, int inEnd, int[] postorder, int postStart, int postEnd){
        if(inStart >= inEnd || postStart >= postEnd){
            return null;
        }
        int val = postorder[postEnd - 1];
        TreeNode root = new TreeNode(val);
        int index = inStart;
        for(int i = inStart; i < inEnd; i++){
            if(inorder[i] == val){
                index = i;
                break;
            }
        }
        root.left = buildTree(inorder, inStart, index, postorder, postStart, postStart + index - inStart);
        root.right = buildTree(inorder, index + 1, inEnd, postorder, postEnd - inEnd +index, postEnd - 1);
        return root;
    }
}

105.从前序与中序遍历序列构造二叉树 

class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        // 闭开区间
        return buildTree(preorder, 0, preorder.length, inorder, 0, inorder.length);
    }

    private TreeNode buildTree(int[] preorder, int preStart, int preEnd, int[] inorder, int inStart, int inEnd){
        if(preStart >=preEnd || inStart >= inEnd){
            return null;
        }
        int val = preorder[preStart];
        TreeNode root = new TreeNode(val);
        int inIndex = inStart;
        for(int i = inStart; i < inEnd; i++){
            if(inorder[i] == val){
                inIndex = i;
                break;
            }
        }
        root.left  = buildTree(preorder, preStart + 1, preStart + 1 + inIndex - inStart,  inorder, inStart, inIndex);
        root.right = buildTree(preorder, preEnd - inEnd  + inIndex +1,preEnd, inorder, inIndex + 1, inEnd);
        return root;
    }
}