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MyBackTracking.java
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175 lines (173 loc) · 5.86 KB
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import java.util.ArrayList;
import java.util.List;
public class MyBackTracking {
public static int ratMaze2Dir(int sr,int sc,int er,int ec) {
if(sr>er||sc>ec)return 0;
if(sr==er&&sc==ec)return 1;
//totalways=down+right
return ratMaze2Dir(sr+1, sc, er, ec)+ratMaze2Dir(sr, sc+1, er, ec);
}
public static void printRatMaze2Dir(int sr,int sc,int er,int ec,String str) {
if(sr>er||sc>ec)return;
if(sr==er&&sc==ec){
System.out.println(str);
return;
}
//down
printRatMaze2Dir(sr+1, sc, er, ec,str+"D");
//right
printRatMaze2Dir(sr, sc+1, er, ec,str+"R");
}
public static void printRatMaze4Dir(int sr,int sc,int er,int ec,String str,boolean[] []check) {
if(sr<0||sc<0||sr>er||sc>ec)return;
if(sr==er&&sc==ec){
System.out.println(str);
return;
}
if(check[sr][sc])return;
check[sr][sc]=true;
//down
printRatMaze4Dir(sr+1, sc, er, ec,str+"D",check);
//right
printRatMaze4Dir(sr, sc+1, er, ec,str+"R",check);
//left
printRatMaze4Dir(sr, sc-1, er, ec,str+"L",check);
//up
printRatMaze4Dir(sr-1, sc, er, ec,str+"U",check);
check[sr][sc]=false;
}
public static void printRatMaze4Dir(int sr,int sc,int er,int ec,String str,int[] []maze) {
if(sr<0||sc<0||sr>er||sc>ec)return;
if(sr==er&&sc==ec){
System.out.println(str);
return;
}
if(maze[sr][sc]==0)return;
//down
printRatMaze4Dir(sr+1, sc, er, ec,str+"D",maze);
//right
printRatMaze4Dir(sr, sc+1, er, ec,str+"R",maze);
}
public static void printRatMaze4Dir(int sr,int sc,int er,int ec,String str,int maze[][],boolean[] []check) {
if(sr<0||sc<0||sr>er||sc>ec)return;
if(sr==er&&sc==ec){
System.out.println(str);
return;
}
if(maze[sr][sc]==0)return;
if(check[sr][sc])return;
check[sr][sc]=true;
//down
printRatMaze4Dir(sr+1, sc, er, ec,str+"D",maze,check);
//right
printRatMaze4Dir(sr, sc+1, er, ec,str+"R",maze,check);
//left
printRatMaze4Dir(sr, sc-1, er, ec,str+"L",maze,check);
//up
printRatMaze4Dir(sr-1, sc, er, ec,str+"U",maze,check);
check[sr][sc]=false;
}
public static void printRatMaze4DirOptimized(int sr,int sc,int er,int ec,String str,int maze[][]) {
if(sr<0||sc<0||sr>er||sc>ec)return;
if(sr==er&&sc==ec){
System.out.println(str);
return;
}
if(maze[sr][sc]==0)return;
if(maze[sr][sc]==-1)return;
maze[sr][sc]=-1;
//down
printRatMaze4DirOptimized(sr+1, sc, er, ec,str+"D",maze);
//right
printRatMaze4DirOptimized(sr, sc+1, er, ec,str+"R",maze);
//left
printRatMaze4DirOptimized(sr, sc-1, er, ec,str+"L",maze);
//up
printRatMaze4DirOptimized(sr-1, sc, er, ec,str+"U",maze);
maze[sr][sc]=1;
}
public static void stringPermutation(String str,String p) {
if(str.equals("")){
System.out.println(p);
return;
}
for(int i=0;i<str.length();i++){
String remaining=str.substring(0,i)+str.substring(i+1);
stringPermutation(remaining, p+str.charAt(i));
}
}
public static void stringPermutation(String str,String p,List<String> l) {
if(str.equals("")){
l.add(p);
return;
}
for(int i=0;i<str.length();i++){
String remaining=str.substring(0,i)+str.substring(i+1);
stringPermutation(remaining, p+str.charAt(i),l);
}
}
public static void kKnights(char[] board[],int sr,int sc) {
// if()
}
public static boolean isSafe(char [][] grid,int row,int col){
int n=grid.length;
//2 up one right
int i=row-2,j=col+1;
if(i>=0&&j<n&&grid[i][j]=='K')return false;
//2 up one left
i=row-2;j=col-1;
if(i>=0&&j>=0&&grid[i][j]=='K')return false;
//2 left one up
i=row-1;j=col-2;
if(i>=0&&j>=0&&grid[i][j]=='K')return false;
//2 left one down
i=row+1;j=col-2;
if(i<n&&j>=0&&grid[i][j]=='K')return false;
//2 right one down
i=row+1;j=col+2;
if(i<n&&j<n&&grid[i][j]=='K')return false;
//2 right one up
i=row-1;j=col+2;
if(i>=0&&j<n&&grid[i][j]=='K')return false;
//2 down one right
i=row+2;j=col+1;
if(i<n&&j<n&&grid[i][j]=='K')return false;
//2 down one left
i=row+2;j=col-1;
if(i<n&&j>=0&&grid[i][j]=='K')return false;
return true;
}
static int max=0;
public static int maxKnightsPlacement(char[] board[],int placed,int cr,int cc) {
int n=board.length;
if(cr==n){
for(char x[]:board){
for(char y:x){
System.out.print(y);
}
System.out.println();
}
System.out.println();
return max=Math.max(max,placed);
}
if(isSafe(board,cr,cc)){
board[cr][cc]='K';
if(cc!=n-1)maxKnightsPlacement(board, placed+1, cr, cc+1);
else maxKnightsPlacement(board, placed+1, cr+1,0);
board[cr][cc]='x';
}
if(cc!=n-1)maxKnightsPlacement(board, placed, cr, cc+1);
else maxKnightsPlacement(board, placed, cr+1,0);
return max=Math.max(max,placed);
}
public static void main(String[] args) {
int row=4,col=4;
char board[][]=new char[row][col];
for(int i=0;i<board.length;i++){
for(int j=0;j<board.length;j++){
board[i][j]='x';
}
}
System.out.println(maxKnightsPlacement(board,0,0,0));
}
}