InFix to PostFix and PreFix conversion [C++]

To Convert from InFix to Postfix:

• Print out constants from InFix directly onto the Postfix output


• For operators, insert them into a stack


•     Before insertion, make sure to pop out (and print to Postfix output) all operator that have higher precedence than that of the operator currently being inserted.


• After the entire Infix is processed, flush the stack (if it is not empty) onto the Postfix output

-In case of InFix to Prefix, we must start processing the string from the RIGHT most to LEFT most instead of the usual LEFT to RIGHT.

-This code can handle only numbers from 0-9 (single digit) and +-*/ operators.

[code language="cpp"]
//Evaluate the given expression
#include<iostream>
#include<stack>
#include<vector>
using namespace std;

//Only single digit numbers permitted

int GetPrecedence(char op)
{
switch (op)
{
case '+':
case '-':
return 1;
case '*':
case '/':
default:
return 2;
}
}
char* ConvertInorderToPreOrder(char* InOrderExp, int Size)
{
stack<char> Operators;
vector<char> PostOrderResult;
for (int i = Size-1; i >=0; i--)
if (InOrderExp[i] >= '0'&& InOrderExp[i] <= '9')
PostOrderResult.push_back(InOrderExp[i]);
else
{
while (!Operators.empty() && GetPrecedence(Operators.top()) >= GetPrecedence(InOrderExp[i]))
{
PostOrderResult.push_back(Operators.top());
Operators.pop();
}
Operators.push(InOrderExp[i]);
}
while (!Operators.empty())
{
PostOrderResult.push_back(Operators.top());
Operators.pop();
}
char *ResultString = (char*)malloc(sizeof(char)*PostOrderResult.size()+1);
memset(ResultString, 0, sizeof(char)*(PostOrderResult.size() + 1));
for (int i = 0; i < PostOrderResult.size(); i++)
ResultString[i] = PostOrderResult[i];
ResultString[PostOrderResult.size()] = '\0';
_strrev(ResultString);
return ResultString;
}
char* ConvertInorderToPostOrder(char* InOrderExp, int Size)
{
stack<char> Operators;
vector<char> PostOrderResult;
for (int i = 0; i < Size; i++)
if (InOrderExp[i] >= '0'&& InOrderExp[i] <= '9')
PostOrderResult.push_back(InOrderExp[i]);
else
{
while (!Operators.empty() && GetPrecedence(Operators.top()) >= GetPrecedence(InOrderExp[i]))
{
PostOrderResult.push_back(Operators.top());
Operators.pop();
}
Operators.push(InOrderExp[i]);
}
while (!Operators.empty())
{
PostOrderResult.push_back(Operators.top());
Operators.pop();
}
char *ResultString = (char*)malloc(sizeof(char)*PostOrderResult.size()+1);
memset(ResultString, 0, sizeof(char)*(PostOrderResult.size()+1));
for (int i = 0; i < PostOrderResult.size(); i++)
ResultString[i] = PostOrderResult[i];
ResultString[PostOrderResult.size()] = '\0';
return ResultString;
}

int main()
{

char InExp[] = "2+3*7-5*2-4/2*5+1-4+2/2+1";
cout << "\nInput: " << InExp;
cout << "\n\n";
cout << "\n\PostFix = " << ConvertInorderToPostOrder(InExp, strlen(InExp));
cout << "\n\PreFix = " << ConvertInorderToPreOrder(InExp, strlen(InExp));
cout << "\n\nEnd of code\n\n";
system("pause");
return 0;
}

[/code]

[Binary Tree] Convert a List to a Binary Search Tree of minimal height

The Problem is to create a binary search tree of minimal possible height from a given list of values. The algorithm for this is quite simple:

1. Sort the items (ascending as well as descending order would do)


2. Use divide and conquer approach for selecting the items for insertion from the array. Given the list, insert its MID item. Then Partition the list into two: 1 list with items less than the MID and another list with items more than MID and recursively process those lists.


3. The crux of this function is as follows:

[code language="cpp"]
void _InsertListRec(int *Arr, int StartIndex, int EndIndex)
{
if (StartIndex > EndIndex) return;
int Mid = 0;
Mid = StartIndex + (EndIndex - StartIndex) / 2;
Insert(Arr[Mid]);
_InsertListRec(Arr, StartIndex, Mid - 1);
_InsertListRec(Arr, Mid + 1, EndIndex);
}

[/code]

The full code is as follows:

[code language="cpp"]
class TreeNode
{
public:
TreeNode *Left, *Right;
int NodalValue;

TreeNode(int ValueParam)
{
NodalValue = ValueParam;
Left = Right = NULL;
}
};

&nbsp;

class BinarySearchTree
{
TreeNode* Root;

void _Insert(TreeNode* Ptr, int ValueParam)
{
//if (!Ptr) return;
if (Ptr->NodalValue == ValueParam) return;
if (ValueParam < Ptr->NodalValue)
{
if (Ptr->Left == NULL) Ptr->Left = new TreeNode(ValueParam);
else _Insert(Ptr->Left, ValueParam);
}
else
{
if (Ptr->Right == NULL) Ptr->Right = new TreeNode(ValueParam);
else _Insert(Ptr->Right, ValueParam);
}
return;
}

void _DFS(TreeNode* Ptr)
{
if (!Ptr) return;
_DFS(Ptr->Left);
cout << " " << Ptr->NodalValue;
_DFS(Ptr->Right);
}

public:
BinarySearchTree()
{
Root = NULL;
}

void Insert(int ValueParam)
{
if (!Root)
{
Root = new TreeNode(ValueParam);
return;
}
_Insert(Root, ValueParam);
}

void DFS()
{
cout << "\nDFS:\n";
_DFS(Root);
}

queue<TreeNode*> NodalQueue;
void BFS()
{
cout << "\nBFS:\n";
if (!Root) return;
while (!NodalQueue.empty())
NodalQueue.pop();
cout << Root->NodalValue << "\n";
NodalQueue.push(Root);
int CLev = 1, NLev = 0;
while (NodalQueue.size() > 0)
{
TreeNode *Ptr = NodalQueue.front();
NodalQueue.pop();
CLev--;
if (Ptr->Left){
cout << Ptr->Left->NodalValue<<" ";
NodalQueue.push(Ptr->Left);
NLev++;
}
if (Ptr->Right)
{
cout << Ptr->Right->NodalValue<<" ";
NodalQueue.push(Ptr->Right);
NLev++;
}
if (!CLev)
{
cout << "\n";
CLev = NLev;
NLev = 0;
}
}

}
void _ClearTree(TreeNode *Ptr)
{
if (!Ptr) return;
if (Ptr->Left){ _ClearTree(Ptr->Left); delete Ptr; }
if (Ptr->Right){ _ClearTree(Ptr->Right); delete Ptr; };
}
void ClearTree()
{
//Post order node deltion
_ClearTree(Root);
Root = NULL;
}

void _InsertListRec(int *Arr, int StartIndex, int EndIndex)
{
if (StartIndex > EndIndex) return;
int Mid = 0;
Mid = StartIndex + (EndIndex - StartIndex) / 2;
Insert(Arr[Mid]);
_InsertListRec(Arr, StartIndex, Mid - 1);
_InsertListRec(Arr, Mid + 1, EndIndex);
}

enum INSERT_OPTION
{
DEFAULT=0,
MIN_HEIGHT=1
};

void InsertList(int *Arr, int Size, INSERT_OPTION CallOption= DEFAULT)
{
ClearTree();

switch (CallOption)
{

case BinarySearchTree::MIN_HEIGHT:
//Sort the list
//->Here assuming that the list is already sorted
_InsertListRec(Arr, 0, Size-1);
break;

case BinarySearchTree::DEFAULT:
for (int i = 0; i < Size; i++)
Insert(Arr[i]);
break;

default:
cout << "\nInvalid Call option\n";
break;
}
}
};

&nbsp;

int main()
{
int Array[] = { 1, 3, 4, 5, 6, 8, 10 };
BinarySearchTree test;

test.InsertList(Array, 7);
test.DFS();
test.BFS();
cout << "\n\nCreating minumum tree:\n";
test.InsertList(Array, 7, BinarySearchTree::MIN_HEIGHT);
test.DFS();
test.BFS();

cout << "\n\nEnd of code";
system("pause");

return 0;
}

[/code]

Anagram Solver

I was coding out a simple string permuting function and I thought of writing out an AnagramSolver just for completion.

The Dictionary can be provided as a wordlist in the form of a text file with a word string per line. You can find several word lists here: http://wordlist.sourceforge.net/

[code language="cpp"]

//Sources
#include<iostream>
#include<string>
#include<fstream>
#include<map>

using namespace std;
class AnagramChecker
{
public:
map<string, bool> Dictionary;
map<string, bool> ResultList;

//Recursive string permuter
void RecurveStrPerm(string Buffer, string Test, int Cur)
{
if (Cur >= Test.length())
{
if (Dictionary.count(Buffer) > 0)
if (ResultList.count(Buffer) == 0)
ResultList[Buffer] = true;
return;
}

for(int i = 0; i <= Buffer.length(); i++)
{
Buffer.insert(i, 1, Test[Cur]);
RecurveStrPerm(Buffer, Test, Cur + 1);
Buffer.erase(i, 1);
}
}

//Build a table out of the strings
void BuildInMemDic()
{
Dictionary.clear();
ifstream DicReader;
DicReader.open("WordList.txt");
string CurrentWord= "";
while (!DicReader.eof())
{
getline(DicReader, CurrentWord);
for (int i = 0; i < CurrentWord.length(); i++)
CurrentWord[i] = tolower(CurrentWord[i]);
Dictionary[CurrentWord] = true;

}
DicReader.close();
}

//Get Result
void GetResult()
{
cout << "\nAnagrams: \n";
for (map<string, bool>::iterator ResultListPtr = ResultList.begin(); ResultListPtr != ResultList.end(); ResultListPtr++)
cout << "\n" << ResultListPtr->first;

}

public:

AnagramChecker()
{
BuildInMemDic();
}

void Find(string Test)
{
ResultList.clear();
int cur = 0, n = Test.length();
RecurveStrPerm("", Test, 0);
GetResult();
}

};

void main()
{
string Test = "Slate";
cout << "\nBuilding In memory Dictionary...";
AnagramChecker AnaObj;
cout << "\n\nInmemory dictionary built!...\n\n";

char ExitChoice = 'n';
while (ExitChoice!='y')
{
cout << "\n\nEnter Anagram: ";
cin >> Test;
for (int i = 0; i < Test.length(); i++)
Test[i] = tolower(Test[i]);

cout << "\n\nAnagrams for " << Test << ":\n\n";
AnaObj.Find(Test);
cout << "\n\nDo you want to continue: y /n :";
cin >> ExitChoice;

}
cout << "\nEnd of code\n";
system("pause");
return;
}

[/code]

The code is NOT optimized. It can be sped up with simple multi-threading, but I have let go of those for simplicity.

Some Binary Tree Tricks

This code can do the following:

• Depth First Search of a Binary Tree


• Breadth First Search of a Binary Tree


• Finding sum of numbers formed by a path from root to leaf, in a binary tree that can contain numbers from 0-9.


• Mirror a binary tree

I have made use of STL - Queues and vectors here.

[code language="cpp"]</pre>
//Source file

#include<iostream>
#include<queue>
#include<vector>
using namespace std;

class Node
{
public:
int Value;
Node *Left, *Right;

Node(int ValueParam)
{
Value = ValueParam;
Left = Right = NULL;
}
};

class BTree
{
private:
Node* Root;

void _Insert(Node* Ptr, int ValueParam)
{
if (Ptr->Value == ValueParam) return;
if (ValueParam < Ptr->Value)
if (Ptr->Left == NULL) Ptr->Left = new Node(ValueParam);
else _Insert(Ptr->Left,ValueParam);
else if (ValueParam >Ptr->Value)
if (Ptr->Right == NULL) Ptr->Right= new Node(ValueParam);
else _Insert(Ptr->Right, ValueParam);
}

void _DFS(Node* Ptr)
{
if (!Ptr) return;
_DFS(Ptr->Left);
cout << " - " << Ptr->Value;
_DFS(Ptr->Right);
}

//Mirroring a Binary Tree
void _Mirror(Node* Ptr)
{
if (!Ptr) return;
_Mirror(Ptr->Left);
_Mirror(Ptr->Right);
Node* Temp = Ptr->Left;
Ptr->Left = Ptr->Right;
Ptr->Right = Temp;
}

public:
BTree()
{
Root = NULL;
}

void Insert(int ValueParam)
{
if (Root == NULL) Root = new Node(ValueParam);
else _Insert(Root, ValueParam);
}

void DFS()
{
cout << "\nDFS:\n";
_DFS(Root);
}
//Breadth First Search
queue<Node*> NodalQueue;
void BFS()
{
cout << "\nBFS:\n";
//Empty the queue
while (!NodalQueue.empty())
NodalQueue.pop();

if (!Root) return;
else
{
cout << " - " << Root->Value;
NodalQueue.push(Root);
}

int CLev = 1, NLev = 0;

//Start working
while (!NodalQueue.empty())
{
Node* Ptr = NodalQueue.front();
NodalQueue.pop();
CLev--;

&nbsp;

if (CLev <= 0)
{
cout << endl;
CLev = NLev;
NLev = 0;
}

if (Ptr->Left)
{
cout << " - " << Ptr->Left->Value;
NodalQueue.push(Ptr->Left);
NLev++;
}
if (Ptr->Right)
{
cout << " - " << Ptr->Right->Value;
NodalQueue.push(Ptr->Right);
NLev++;
}

}
}

//Get Numbers
vector<vector<int>> NumberMap;
void GetNumberMap()
{
cout << "\nNumberMap:\n";
NumberMap.clear();
queue<Node*> NumNodalQueue;
if (!Root) return;
else
{
NumNodalQueue.push(Root);
vector<int> RootStage;
RootStage.push_back(Root->Value);
NumberMap.push_back(RootStage);
}

//Start working
int Stage = 0;
int CLev = 1;
int NLev = 0;
while (!NumNodalQueue.empty())
{
Node* Ptr = NumNodalQueue.front();
vector<int> NewStage;
NumNodalQueue.pop();
CLev--;
if (CLev<=0)
{
Stage++;
NumberMap.push_back(NewStage);
CLev = NLev;
NLev = 0;
}
if (Ptr->Left)
{
NumberMap[Stage].push_back(Ptr->Left->Value);
NumNodalQueue.push(Ptr->Left);
NLev++;
}
if (Ptr->Right)
{
NumberMap[Stage].push_back(Ptr->Right->Value);
NumNodalQueue.push(Ptr->Right);
NLev++;
}
}

//Numbermap is ready
//Calcualte combinations from NumberMap
NumberMap.pop_back();
GetCombinations();
}

void GetCombinations()
{
GlobalTot = 0;
RecCombi();
}

long int fnPow(int Base, int Power)
{
if (Power == 0) return 1;
return Base*fnPow(Base, Power - 1);
}

long int GlobalTot = 0;
void RecCombi(vector<int>* Temp=NULL, int Stage=0)
{
if (Temp && Stage == NumberMap.size())
{
cout << "\n";
for (int i = 0; i < Temp->size(); i++)
{
long int pval = fnPow(10, (Temp->size() - 1 - i));
GlobalTot += (*Temp)[i]*(pval);
cout << " " << (*Temp)[i];
}
cout << "\n";
//Adding number to Global
}
if (Stage < NumberMap.size())
{
if (!Temp) Temp = new vector<int>();
for (int i = 0; i < NumberMap[Stage].size(); i++)
{
Temp->push_back(NumberMap[Stage][i]);
RecCombi(Temp, Stage + 1);
Temp->pop_back();
}
}
}

void Mirror()
{
_Mirror(Root);
cout << "\nTree Mirrored\n";
}

};

int main()
{
BTree MyTree;

MyTree.Insert(6);
MyTree.Insert(2);
MyTree.Insert(10);
MyTree.Insert(0);
MyTree.Insert(4);
MyTree.Insert(8);
MyTree.Insert(15);
MyTree.Insert(-1);
MyTree.Insert(1);
MyTree.Insert(3);
MyTree.Insert(5);
MyTree.Insert(7);
MyTree.Insert(9);
MyTree.Insert(12);
MyTree.Insert(20);
MyTree.DFS();
MyTree.BFS();
MyTree.Mirror();
MyTree.DFS();
MyTree.BFS();
MyTree.GetNumberMap();

cout << "\nGloabl total =" << MyTree.GlobalTot << endl;
cout << "\n\nEnd of code\n\n";
system("pause");

return 0;
}

&nbsp;
<pre>
[/code]

Please note: The third problem (finding sum of numbers) does not require a binary search tree which has been used here. A simple binary tree would do. But the code would be the same whether the tree is a BST or not.