more backtracking

Author: dhananjay-ng

Diff for: src/main/java/problems/onRecursionAndDp/backtracking/Suduko.java

@@ -0,0 +1,51 @@
+package problems.onRecursionAndDp.backtracking;
+
+import java.util.ArrayList;
+
+public class Suduko {
+    public class Solution {
+        public void solveSudoku(ArrayList<ArrayList<Character>> a) {
+            for(int i=0;i<9;i++) {
+                for(int j=0;j<9;j++){
+                    solve(a, i,j);
+                }
+            }
+        }
+
+        public boolean solve(ArrayList<ArrayList<Character>> a, int row, int col) {
+            if(col >= 9){ col=0;row++;}
+            if(row >= 9) return true;
+            if(Character.isDigit(a.get(row).get(col))) {
+                return solve(a, row, col+1);
+            }
+
+            for(int i=1;i<=9;i++) {
+                if(isValid(a, row, col, (char)('0'+i))){
+                    a.get(row).set(col, (char)('0'+i));
+                    if(solve(a, row, col+1)) return true;
+                }
+            }
+            a.get(row).set(col, '.');
+            return false;
+        }
+
+        boolean isValid(ArrayList<ArrayList<Character>> a, int row, int col, Character x) {
+            int rowst = (row/3)*3;
+            int colst = (col/3)*3;
+            for(int i=rowst;i<rowst+3;i++){
+                for(int j=colst;j<colst+3;j++) {
+                    if(a.get(i).get(j).equals(x)) return false;
+                }
+            }
+
+            for(int j=0;j<9;j++){
+                if(a.get(row).get(j).equals(x)) return false;
+            }
+            for(int i=0;i<9;i++){
+                if(a.get(i).get(col).equals(x)) return false;
+            }
+            return true;
+        }
+    }
+
+}

Diff for: src/main/java/problems/onRecursionAndDp/backtracking/VisiteAllMazePaths.java

@@ -0,0 +1,40 @@
+package problems.onRecursionAndDp.backtracking;
+
+public class VisiteAllMazePaths {
+    public class Solution {
+        int count;
+        public int solve(int[][] A) {
+            this.count = 0;
+            for(int i=0;i<A.length;i++){
+                for(int j=0;j<A[0].length;j++){
+                    if(A[i][j]==1) {
+                        solve(A, i, j, 0);
+                        return this.count;
+                    }
+                }
+            }
+            return this.count;
+        }
+
+        public boolean solve(int [][] A, int x, int y, int visited) {
+            if(x<0 || x>=A.length || y<0 || y> A[0].length || A[x][y] == -1 || A[x][y] == -2) return false;
+            visited++;
+            if(A[x][y] == 2) {
+                if(visited == A.length*A[0].length) {
+                    this.count++;
+                }
+                visited++;
+                return false;
+            }
+            A[x][y] = -2;
+            solve(A,x+1,y, visited);
+            solve(A,x-1,y, visited);
+            solve(A,x,y+1, visited);
+            solve(A,x,y-1, visited);
+
+            visited--;
+            return false;
+        }
+    }
+
+}