剑指offer题目61-67

面试题61：把二叉树打印成多行

public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
         travel(pRoot,res,0);
         return res;
    }
    public void travel(TreeNode cur,ArrayList<ArrayList<Integer>> res,int level){
        if(cur==null) return;
        if(res.size()<=level){
            ArrayList<Integer> newLevel = new ArrayList<Integer>();
            res.add(newLevel);
        }
        ArrayList<Integer> col = res.get(level);
        col.add(cur.val);
        travel(cur.left,res,level+1);
        travel(cur.right,res,level+1);
    }
}

面试题62：序列化二叉树

import java.util.Queue;
import java.util.LinkedList;
public class Solution {
    String Serialize(TreeNode root) {
        if(root == null) return "#!";
        String res = root.val + "!";
        res += Serialize(root.left);
        res += Serialize(root.right);
        return res;
    }
    TreeNode Deserialize(String str) {
       String[] values = str.split("!");
       Queue<String> queue = new LinkedList<String>();
       for(int i=0;i<values.length;i++){
            queue.offer(values[i]);
       }
       return recover(queue);
    }
    TreeNode recover(Queue<String> queue){
        String value = queue.poll();
        if(value.equals("#")){
            return null;
        }
        TreeNode root = new TreeNode(Integer.valueOf(value));
        root.left = recover(queue);
        root.right = recover(queue);
        return root;
    }
}

面试题63：二叉搜索树的第K个节点

import java.util.ArrayList;
public class Solution {
    public ArrayList<TreeNode> res = new ArrayList<TreeNode>();
    TreeNode KthNode(TreeNode pRoot, int k)
    {
        if(pRoot==null || k==0) return null;
        inorderTra(pRoot);
        if(k<=0 || k>res.size()) return null;
        return res.get(k-1);
    }
     public void inorderTra(TreeNode root){
        if(root == null) return ;
        inorderTra(root.left);
        res.add(root);
        inorderTra(root.right);
    }
}
补充第二种做法：
public class Solution {
    public TreeNode res ;
    public int cnt = 0;
    TreeNode KthNode(TreeNode pRoot, int k)
    {
        cnt = k;
        if(pRoot == null) return pRoot;
           help(pRoot);
        return res;
    }
    public void help(TreeNode p){
        if(p.left!=null){
            help(p.left);
        }
        cnt--;
        if(cnt == 0){
            res = p;
            return;
        }
        if(p.right!=null){
             help(p.right);
        }
        return;
    }
}

面试题64：数据流中的中位数

import java.util.PriorityQueue;
import java.util.Collections;
public class Solution {
    private PriorityQueue<Integer> minHeap = new PriorityQueue<Integer>();
    private PriorityQueue<Integer> maxHeap = new PriorityQueue<Integer>(5000,Collections.reverseOrder());
    public void Insert(Integer num) {
        if(maxHeap.isEmpty() || num<maxHeap.peek()){
            maxHeap.offer(num);
        }else{
            minHeap.offer(num);
        }
        if(maxHeap.size() > minHeap.size() + 1){
            minHeap.offer(maxHeap.poll());
        }else if(minHeap.size() > maxHeap.size()){
            maxHeap.offer(minHeap.poll());
        }
    }
    public Double GetMedian() {
        if(maxHeap.size() > minHeap.size()){
            return (double)maxHeap.peek();
        }else{
            return (maxHeap.peek() + minHeap.peek())/2.0;
        }
    }
}

面试题65：滑动窗口的最大值

import java.util.Deque;
import java.util.ArrayDeque;
import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> maxInWindows(int [] num, int size)
    {
        ArrayList<Integer> res = new ArrayList<Integer>();
        if(num == null || size<=0){
            return res;
        }
        int n = num.length;
        Deque<Integer> queue = new ArrayDeque<Integer>();
        for(int i=0;i<num.length;i++){
            while(!queue.isEmpty() && queue.peek()<i-size+1){
                queue.poll();
            }
            while(!queue.isEmpty() && num[queue.peekLast()]<num[i]){
                queue.pollLast();
            }
            queue.offer(i);
            if(i>=size-1){
                res.add(num[queue.peek()]);
            }
        }
        return res;
    }
}

面试题66：矩阵中的路径

为什么这么写就不对？
public class Solution {
    public boolean hasPath(char[] matrix, int rows, int cols, char[] str)
    {
        if(matrix==null||rows<1||cols<1||str==null) return false;
        boolean[] visited = new boolean[matrix.length];
        for(int i=0;i<rows;i++){
            for(int j=0;j<cols;j++){
                if(dfs(matrix,rows,cols,i,j,0,str,visited)){
                    return true;
                }
            }
        }
        return false;
    }
    public boolean dfs(char[] matrix,int rows,int cols,int i,int j,int k,char[] str,boolean[] visited){
        if(k == str.length - 1){
            return true;
        }
        int index = i*cols+j;
        boolean hasPath = false;
        if(i>=0&&i<rows&&j>=0&&j<cols&&matrix[index]==str[k]&&visited[index]==false){
            visited[index] = true;
            hasPath = dfs(matrix,rows,cols,i,j+1,k+1,str,visited)
                    ||dfs(matrix,rows,cols,i,j-1,k+1,str,visited)
                    ||dfs(matrix,rows,cols,i+1,j,k+1,str,visited)
                    ||dfs(matrix,rows,cols,i-1,j,k+1,str,visited);
            visited[index] = false;
        }
        return hasPath;
    }
}
这样写就可以
public class Solution {
    public boolean hasPath(char[] matrix, int rows, int cols, char[] str) {
        int flag[] = new int[matrix.length];
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                if (helper(matrix, rows, cols, i, j, str, 0, flag))
                    return true;
            }
        }
        return false;
    }
    private boolean helper(char[] matrix, int rows, int cols, int i, int j, char[] str, int k, int[] flag) {
        int index = i * cols + j;
        if (i < 0 || i >= rows || j < 0 || j >= cols || matrix[index] != str[k] || flag[index] == 1)
            return false;
        if(k == str.length - 1) return true;
        flag[index] = 1;
        if (helper(matrix, rows, cols, i - 1, j, str, k + 1, flag)
                || helper(matrix, rows, cols, i + 1, j, str, k + 1, flag)
                || helper(matrix, rows, cols, i, j - 1, str, k + 1, flag)
                || helper(matrix, rows, cols, i, j + 1, str, k + 1, flag)) {
            return true;
        }
        flag[index] = 0;
        return false;
    }
}

面试题67：机器人的运动范围

public class Solution {
    public int movingCount(int threshold, int rows, int cols)
    {
        boolean[] visited = new boolean[rows*cols];
        int res = count(0,0,rows,cols,threshold,visited);
        return res;
    }
    public int count (int i,int j,int rows,int cols,int threshold,boolean[] visited){
        int cnt = 0;
        int index  = i*cols+j;
        if(check(threshold,i,j,rows,cols,visited) == true){
            visited[index] = true;
            cnt = 1 + count(i+1,j,rows,cols,threshold,visited)
                    + count(i-1,j,rows,cols,threshold,visited)
                    + count(i,j+1,rows,cols,threshold,visited)
                    + count(i,j-1,rows,cols,threshold,visited);
        }
        return cnt;
    }
    public boolean check(int threshold,int i,int j,int rows,int cols,boolean[] visited){
        int valRow = getVal(i);
        int valCol = getVal(j);
        if(i>=0&&i<rows&&j>=0&&j<cols&&valRow+valCol<=threshold&&visited[i*cols+j]==false){
            return true;
        }
        return false;
    }
    public int getVal(int i){
        int val = 0;
        while(i>0){
            val += i%10;
            i /= 10;
        }
        return val;
    }
}

​