Min moves to move Knight from one grid to another on a NxN Chess board.

TO find the minimum moves required to move a Knight on a NxN chess board
from position (x,y) to (a,b).

The problem is solved using Graphs. The min number of moves can be computed with running BFS on graph generated with NxN nodes. The adjacency between the vertexesof the graph is computed using the movement of the horse.

Try running the Computation of Adjacency and min distance code online:http://codepad.org/yZDbgECz

N=8 and the vertexes are numbered in the below order.

  00 01 02 03 04 05 06 07
  08 09 10 11 12 13 14 15
  16 17 18 19 20 21 22 23
  24 25 26 27 28 29 30 31
  32 33 34 35 36 37 38 39
  40 41 42 43 44 45 46 47
  48 49 50 51 52 53 54 55

  56 57 58 59 60 61 62 63  

#include <iostream> #include <queue> using namespace std; #define GRID 8 #define ADJMATRIX 64 //(GRID*GRID) /*************************************************************************** TO find the minimum moves required to move a Knight on a NxN chess board from position (x,y) to (a,b). Note: Assumption =for a 8x8 matrix (x,y) range is (0,0) to (7,7). Author: Thejas P M *****************************************************************************/ class Node { public: int Dist; Node(int d=0) { Dist=d; } }; void possibleKnightMoves(int x, int y,Node arr[64][64]) { int xPlus2 = x+2; int xMinus2 = x-2; int xPlus1 = x+1; int xMinus1 = x-1; int yPlus2 = y+2; int yMinus2 = y-2; int yPlus1 = y+1; int yMinus1 = y-1; int current = y*GRID+x; arr[current][current].Dist=0; if(xPlus2 < GRID && yPlus1 < GRID) { int adjVtx = yPlus1*GRID+xPlus2; arr[current][adjVtx].Dist=1; } if(xPlus2 < GRID && yMinus1 >= 0) { int adjVtx = yMinus1*GRID+xPlus2; arr[current][adjVtx].Dist=1; } if(xMinus2 >= 0 && yPlus1 < GRID) { int adjVtx = yPlus1*GRID+xMinus2; arr[current][adjVtx].Dist=1; } if(xMinus2 >= 0 && yMinus1 >= 0) { int adjVtx = yMinus1*GRID+xMinus2; arr[current][adjVtx].Dist=1; } if(xPlus1 < GRID && yPlus2 < GRID) { int adjVtx = yPlus2*GRID+xPlus1; arr[current][adjVtx].Dist=1; } if(xPlus1 < GRID && yMinus2 >= 0) { int adjVtx = yMinus2*GRID+xPlus1; arr[current][adjVtx].Dist=1; } if(xMinus1 >= 0 && yPlus2 < GRID) { int adjVtx = yPlus2*GRID+xMinus1; arr[current][adjVtx].Dist=1; } if(xMinus1 >= 0 && yMinus2 >= 0) { int adjVtx = yMinus2*GRID+xMinus1; arr[current][adjVtx].Dist=1; } return; } int** BFSAdj(Node arr[64][64], int& vtx,int& vtxCount) { /* Step 1: Colour all the nodes in the Storage structure as White(0) and parents to -1 Step 2: Start with the vtx passed onto the function set its Distance to 0 i.e Storage[vtx][2]=0 Step 3: Initialize a Queue, ENQUE the vtx onto Q Step 4: While Queue not empty do Let VtxTemp = DEQUE from Q Let S array = all Vertexes Adjacent to VtxTemp For each vertex in S array if Storage[Si][0] == White Change colour Storage[Si][0] == Grey Update Distance Storage[Si][2] == Storage[VtxTemp][2] + 1 Update parent Storage[Si][2] = VtxTemp ENQUE Si Storage[VtxTemp][1]=2 Step 5: Done */ if(vtxCount <=0 || vtx > vtxCount) { cout<<"CHECK the INPUT TO BFS"<<endl; return NULL; } int **Storage = NULL; Storage = new int*[vtxCount]; int i=0; for(i=0;i<vtxCount;++i) { Storage[i]=new int[3]; Storage[i][0]=0; //holds the colour of the node 0-White,1-Grey,2-Black Storage[i][1]=-1; //Parent Node Storage[i][2]=99; //Distance //cout<<Storage[i][0]<<endl<<Storage[i][1]<<endl<<Storage[i][2]<<endl<<endl; } Storage[vtx][2]=0; int array[64]; int temp_count=0; std::queue<int> bfsQ; bfsQ.push(vtx); while(bfsQ.size() > 0) { int vtxTemp = bfsQ.front(); array[temp_count++]=vtxTemp; bfsQ.pop(); /* Node *sArray =arr[vtxTemp-1].next; while (sArray != NULL) { if(Storage[sArray->value-1][0] == 0)//white {cout<<"sArray->value="<<sArray->value<<endl; Storage[sArray->value-1][0]=1; Storage[sArray->value-1][1]=vtxTemp; Storage[sArray->value-1][2]=Storage[vtxTemp-1][2] + 1; bfsQ.push(sArray->value); cout<<Storage[sArray->value-1][0]<<" "<<Storage[sArray->value-1][1]<<" "<<Storage[sArray->value-1][2]<<endl<<endl; } sArray=sArray->next; } */ for(int j=0;j<ADJMATRIX;++j) { if(arr[vtxTemp][j].Dist==1) { if(Storage[j][0] == 0)//white { cout<<"vtxTemp,j="<<vtxTemp<<","<<j<<endl; Storage[j][0]=1; Storage[j][1]=vtxTemp; Storage[j][2]=Storage[vtxTemp][2] + 1; bfsQ.push(j); //cout<<" "<<j; // cout<<"-----"<<j<<"------"<<endl<<Storage[j][0]<<"\n"<<Storage[j][1]<<" \n"<<Storage[j][2]<<endl<<endl; } } } Storage[vtxTemp][0]=2; } //Print nodes the entered the Q /*cout<<"\nPOP ORDER\n"; for(int i=0;i<temp_count;++i) cout<<" "<<array[i]; cout<<"\n";*/ return Storage; } int getMove(int** res,int vtxSource,int vtxDst) { cout<<"\n PATH = "<<vtxDst<<"<=="; if(res[vtxDst][2]==99) { return -1; } int result=res[vtxDst][2]; while(res[vtxDst][1]!=-1) { vtxDst=res[vtxDst][1]; cout<<vtxDst<<"<=="; } cout<<endl; return result; } /*NxN Knight shortest path / Min moves There are NxN nodes in total two nodes [(x,y) and (a,b)] are connected if a,b < GRID and (a,b) is in {(x+1,y+2),(x+1,y-2),(x+2,y+1),(x+2,y-1),(x-2,y-1),(x-2,y+1),(x+2,y+1),(x+1,y-1)} the nodes are numbered in this order 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 The conversion from the x,y cordinates to the nodes Formula [vertex = (x*GRID+j)] similarly x,y = */ int main() { Node arr[ADJMATRIX][ADJMATRIX]; for(int i=0;i<GRID;++i) { for(int j=0;j<GRID;++j) { possibleKnightMoves(i,j,arr); } } int x = 7, y = 3,vtxSource = y*GRID+x; int xa = 7,ya=7,vtxDst=ya*GRID+xa,count =ADJMATRIX; int** resultSet= BFSAdj(arr,vtxSource,count); // Find min moves cout<<"ANSWER = "<<getMove(resultSet,vtxSource,vtxDst); //Print adjacencyMatrix /*for(int i=0;i<count;++i) { cout<<""<<i<<"\t"; } cout<<endl<<endl; for(int i=0;i<count;++i) { for(int j=0;j<count;++j) { cout<<arr[i][j].Dist<<"\t"; } cout<<endl; }*/ //PRINT BFS MATRIX /* cout<<" --- Result --"<<endl; for(int i=0;i<count;++i) { cout<<"a["<<i<<"]\t"; } cout<<endl; for(int j=0;j<3;++j) { for(int i=0;i<count;++i) { cout<<resultSet[i][j]<<"\t\t"; } cout<<endl; } */ return 0; }

what is the difference between usage of a "macro" and a "typedef"?

In the first look it seems that a typedef is totally redundant as its job can be done using a macro in c++. the actual difference and the need for typedef can be clearly understood considering the usage of both these with pointers. All compiler does for a macro is to blindly replace the occurrences with the specified equivalent value before the compilation process. In case of the typedef c++ treats it as an alias in compile time for its definition.

#define intptr1 int* typedef int* intptr; Consider the below example: are they the same to the compiler? NO //are following two equivalent? intptr1 a,b; intptr2 a,b; Consider the macro defnition, intptr1 is simply replaced with int* int* a, b; // intptr replaced by int* Which means that we are declaring variable 'a' of type "int*" and variable 'b'of type "int". Something which we certainly didn't mean. The second definition involves intptr2, which is a typedef to int*. typedefs are handelled by the C++ compiler,
and they are treated identical to the type that they stand for. Thus, there is not just a "textual substritution", but much more than that: int *a, *b; // intptr2 is treated identical to int*


another fail case:


#define intptr1 int*
typedef int* intptr2;
//Are these equivalent?
const intptr1 x;
const intptr2 y;

Storage Class Specifiers in C++

Storage specifiers specify the scope linkage and lifetime of a variable.
The default storage specifier for all function parameters and variables is auto.


auto -  specifies an automatic variable. The storage scope is limited to the scope of the inner braces the variable is declared.


register - this indicates the compiler to store the variable in the CPU registers to allow fast access. However the modern compilers are smart enough= to figure which variables have to be stored in the registers.


mutable - denotes that the member can be modified even if the containing object is a const.


static - denotes a variable with static linkage, function parameters should never be made static.


extern - Denotes the variable is declared in another file.

Simple Game - Beginner C++

Guess the number game

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

#include <iostream> #include <stdlib.h> #include <time.h> //Author Thejas using namespace std; int generateRandomNumber(); int main() {     srand(time(NULL));     int secret = generateRandomNumber();     int inputVar = -1;     cout<<"~~~~~~~~~~~Guess the Magic Number Game (1 to 100)~~~~~~~~~~~"<<secret<<endl;     do     {         cout<<"Enter the number "<<endl;         if(!(cin>> inputVar))         {             cout<<"You should only enter integers between 1 to 100"<<endl;             cin.clear();             cin.ignore(1000,'\n');         }         else if(inputVar > 100 || inputVar < 1)         {             cout<<"You should only enter integers between 1 to 100"<<endl;             cin.clear();             cin.ignore(1000,'\n');         }else if(inputVar > secret)         {             cout<<"The secret number is lesser"<<endl;         }else if(inputVar < secret)         {             cout<<"The secret number is greater"<<endl;         }else{             cout<<"You have fount the Secret number "<<secret<<endl;             cout<<"Fireworks Busrsting!!!!!!!"<<endl;             break;         }     }while(true);     return 1; } int generateRandomNumber() {     int randomNum = (rand()%100)+1;     return randomNum; }