第 11 屆 iThome 鐵人賽

DAY 15

自我挑戰組

練習程式系列第 15 篇

java ，Binary Search 和、計算時間、記憶體和 c++ tree traversal 、 Binary Search Tree、infix、prefix、postfix

11th鐵人賽

tedtedtedtedted

2019-09-29 00:14:52

1299 瀏覽

分享至

看網路上大大們的文章和影片，做些紀錄。
以下內容來自網路上大大們的文章。
紀錄程式來源。稍微修改，print 觀察

Binary Search

程式來源:
二元搜索法(Binary Search)
java测试方法运行时间 System.currentTimeMillis();
[JAVA]記憶體量測與執行時間量測
 百萬位元組
整理:
1 currentTimeMillis()返回毫秒時間，返回的值是與1970年1月1日午夜之間的時間差

2 runtime用法還不知道

3 結果不太清楚，用的是雲端環境，看起來是非遞迴比較快，記憶體一樣

遞迴:

import java.util.Arrays;
import java.util.Scanner;

class DivideAndConquer {
    static public int Search(int[] array, int num)
    {
        return Search(array, num, 0, array.length - 1);
    }
 
    static public int Search(int[] array, int num, int left, int right)
    {
        if (left > right)
            return -1;
 
        int middle = (right + left) / 2;
 
        if (array[middle] == num)
            return middle;
 
        if (array[middle] > num)
            return Search(array, num, left, middle - 1);
 
        return Search(array, num, middle + 1, right);
    }
}

class Main {
  private static final long MEGABYTE = 1024L * 1024L;

  public static long bytesToMegabytes(long bytes) {
   return bytes / MEGABYTE;
  }

  public static void main(String[] args) {
     long startTime = System.currentTimeMillis();

     int array[] = {1,3,5,7,9,11,13,15,17,19,21,23,25,27,31,33,35,37,39}; 
     int num = 1;
     int result = DivideAndConquer.Search(array,num);
     for(int i =0;i<=2047483647;i++){
        result = DivideAndConquer.Search(array,num);
     }
     System.out.println(result); 

     //計算記憶體
     // Get the Java runtime
     Runtime runtime = Runtime.getRuntime();
     // Run the garbage collector
     runtime.gc();
     // Calculate the used memory
     long memory = runtime.totalMemory() - runtime.freeMemory();
     System.out.println("Used memory is byte: " + memory);
     System.out.println("Used memory is Megabyte: " +  bytesToMegabytes(memory));
     
     //總共花費時間
     long stopTime = System.currentTimeMillis();
     long elapsedTime = stopTime - startTime;
     //System.out.println("stopTime: " + stopTime);
     System.out.println("總共花費時間:(毫秒)" + elapsedTime);
  }
}

0
Used memory is byte: 512384
Used memory is Megabyte: 0
總共花費時間:(毫秒)65118

實機:(改成KB)

Used memory is byte: 707336
Used memory is Kilobyte: 690
總共花費時間:(毫秒) 8413

非遞迴:

import java.util.Arrays;
import java.util.Scanner;

class Iterative {
    static public int Search(int[] array, int num)
    {
        int left = 0, right = array.length - 1;
        while (left <= right)
        {
            int middle = (right + left) / 2;
 
            if (array[middle] == num)
                return middle;
 
            if (array[middle] > num)
                right = middle - 1;
            else
                left = middle + 1;
        }
        return -1;
    }
}

class Main {
  private static final long MEGABYTE = 1024L * 1024L;

  public static long bytesToMegabytes(long bytes) {
   return bytes / MEGABYTE;
  }

  public static void main(String[] args) {
     long startTime = System.currentTimeMillis();

     int array[] = {1,3,5,7,9,11,13,15,17,19,21,23,25,27,31,33,35,37,39}; 
     int num = 1;
     int result = Iterative.Search(array,num);

     for(int i =0;i<=2047483647;i++){
        result = Iterative.Search(array,num);
     }
     System.out.println(result); 
     
     //計算記憶體
     // Get the Java runtime
     Runtime runtime = Runtime.getRuntime();
     // Run the garbage collector
     runtime.gc();
     // Calculate the used memory
     long memory = runtime.totalMemory() - runtime.freeMemory();
     System.out.println("Used memory is byte: " + memory);
     System.out.println("Used memory is Megabyte: " +  bytesToMegabytes(memory));

     
     //總共花費時間
     long stopTime = System.currentTimeMillis();
     long elapsedTime = stopTime - startTime;
     //System.out.println("stopTime: " + stopTime);
     System.out.println("總共花費時間:(毫秒) " + elapsedTime);

  }
}

0
Used memory is byte: 512328
Used memory is Megabyte: 0
總共花費時間:(毫秒) 48766

實機:(改成KB)

Used memory is byte: 707336
Used memory is Kilobyte: 690
總共花費時間:(毫秒) 8213

其他C/C++的:
【c/c++學習筆記】如何測量一段程式碼的執行時間?
C/C++ 語言測量時間函數，評估程式執行效能方法整理
 g++ error: ‘malloc’ was not declared in this scope
可能要加

<stdlib.h>

tree traversal: Preorder, Inorder, Postorder

Binary tree traversal: Preorder, Inorder, Postorder

程式:
https://gist.github.com/mycodeschool/10016271

#include<iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace std;

struct Node {
  int data;
  struct Node * left;
  struct Node * right;
};

void Preorder(struct Node * root) {
  if (root == NULL) return;
  printf("%d ", root - > data);
  Preorder(root - > left);
  Preorder(root - > right);
}

void Inorder(Node * root) {
  if (root == NULL) return;
  Inorder(root - > left);
  printf("%d ", root - > data);
  Inorder(root - > right);
}

void Postorder(Node * root) {
  if (root == NULL) return;
  Postorder(root - > left);
  Postorder(root - > right);
  printf("%d ", root - > data);
}

Node * Insert(Node * root, int data) {
  if (root == NULL) {
    root = new Node();
    root - > data = data;
    root - > left = root - > right = NULL;
  } else if (data <= root - > data)
    root - > left = Insert(root - > left, data);
  else
    root - > right = Insert(root - > right, data);
  return root;
}

int main() {
  Node * root = NULL;
  root = Insert(root, 9);
  root = Insert(root, 4);
  root = Insert(root, 8);
  root = Insert(root, 7);
  root = Insert(root, 18);
  root = Insert(root, 1);
  //Print Nodes in Preorder.
  cout << "Preorder: ";
  Preorder(root);
  cout << "\n";
  //Print Nodes in Inorder
  cout << "Inorder: ";
  Inorder(root);
  cout << "\n";
  //Print Nodes in Postorder
  cout << "Postorder: ";
  Postorder(root);
  cout << "\n";
}

結果:

Preorder: 9 4 1 8 7 18
Inorder: 1 4 7 8 9 18
Postorder: 1 7 8 4 18 9

Binary Search Tree

Level Order Traversal:

參考:
Binary tree: Level Order Traversal

程式來源：mycodeschool/BST_CPP.cpp

教學來源：Binary Search Tree: Intro(簡介)

#include<iostream>
using namespace std;

struct BstNode {
  int data;
  BstNode * left;
  BstNode * right;
};
//create a new Nod
BstNode * GetNewNode(int data) {
  BstNode * newNode = new BstNode();
  newNode - > data = data;
  newNode - > left = newNode - > right = NULL;
  return newNode;
}

//insert data in BST
BstNode * Insert(BstNode * root, int data) {
  if (root == NULL) {
    root = GetNewNode(data);
  } else if (data <= root - > data) {
    root - > left = Insert(root - > left, data);
  } else {
    root - > right = Insert(root - > right, data);
  }
  return root;
}
//search
bool Search(BstNode * root, int data) {
  if (root == NULL) {
    return false;
  } else if (root - > data == data) {
    return true;
  } else if (data <= root - > data) {
    return Search(root - > left, data);
  } else {
    return Search(root - > right, data);
  }
}
// FindMin
int FindMin(BstNode * root) {
  if (root == NULL) {
    cout << "Error: Tree is empty\n";
  } else if (root - > left == NULL) {
    return root - > data;
  }
  // search in left subtree
  return FindMin(root - > left);
}

//FindHeight
int FindHeight(BstNode * root) {
  if (root == NULL)
    return -1;
  return max(FindHeight(root - > left), FindHeight(root - > right)) + 1;
}

int main() {
  BstNode * root = NULL;
  root = Insert(root, 15);
  root = Insert(root, 10);
  root = Insert(root, 20);
  root = Insert(root, 25);
  root = Insert(root, 8);
  root = Insert(root, 12);
  root = Insert(root, 30);
  //搜尋數字
  int number;
  cout << "搜尋數字:\n";
  cin >> number;
  //結果:
  if (Search(root, number) == true) cout << "Found\n";
  else cout << "Not Found\n";

  //FindMin 找最小值
  cout << "最小值:" << FindMin(root - > left) << "\n";

  //樹的高度:
  cout << "樹的高度:" << FindHeight(root) << "\n";
}

結果：

搜尋數字:
12
Found
最小值:8
樹的高度:3

infix、prefix、postfix

來源【小馬的資結演算法秘笈】(12) 將infix表達式轉postfix(即普通四則運算式轉逆波蘭表達式)
Infix, Prefix and Postfix
Evaluation of Prefix and Postfix expressions using stack
Infix to Postfix using stack

整理
1
operator -- > 運算子 -->加減乘除
operand -- >運算數 -- >123

2
operator優先順序
1 括號
2 右到左的operator(指數)
3 乘除
4 加減

3
Evaluation of Prefix and Postfix expressions using stack

教學 教了 怎麼計算 postfix
像是 postfix_string = "23-54*+"

創建一個stack S
//由左而右掃描
for i = 0 to length(postfix_string)-1
{
      if(postfix_string[i] is operand)  //如果是數字:123
        Push(postfix_string[i])
      else if (postfix_string[i] is operator){ //如果是運算子+-*/
        Pop(operand2)
        Pop(operand1)
        result = operand1 postfix_string[i] operand2   // 先pop的放後面
        // 像是(2-3) 變成 23- ， 先pop的是3 ， 所以就會是2-3
        //不過如果是 -23 (prefix) ， 先pop的是2 ，但是 還是2-3 (先pop的放前面?)(prefix不知道怎運作)
        Push(result)
      }
      
}
return top of stack S

4
Infix to Postfix using stack:
Infix to Postfix using stack

程式碼:
mycodeschool/InfixToPostfix.cpp

有些小錯誤，所以有人修改了:
ms1797/InfixToPostfix.cpp

錯的地方應該就是這邊要加break:

	switch(op)
	{
	case '+':
	case '-':
		weight = 1;
		break;
	case '*':
	case '/':
		weight = 2;
		break;
	case '^':
		weight = 3;
        break;
	}

還有$符號不知道是什麼，先換成^ (XOR符號???)

結果:

5
Palindrome Number 回文數字
像是abcdcba 或是 121 都是回文
題目:Palindrome Number

題目是判斷數字是不是回文，如果是就true ，不是就false

先踢掉一些狀況
像是 -2(負數)  、  100 (結尾有0 但不是0的數字)

有兩種 回文狀況
12321 或是 1221

範例解答是這樣寫:
        int revertedNumber = 0;
        while(x > revertedNumber) {
            revertedNumber = revertedNumber * 10 + x % 10;
            x /= 10;
        }
順序-->
x= 12321  , revertedNumber=0
x= 1232  , revertedNumber=1
x= 123  , revertedNumber=12
x= 12  , revertedNumber=123

順序-->
x= 1221  , revertedNumber=0
x= 122  , revertedNumber=1
x= 12  , revertedNumber=12

最後在判斷
return x == revertedNumber || x == revertedNumber/10;
12==12
或是
12 == 123/10

6
Valid Parentheses
這題是判斷括號正不正確:
([)] 、((()) 這種都是錯的

解法就是用hashmap的方式，如果ClosingBracket 對的到 stack top 的 OpeningBracket ，就是true