java - Iterative brute-force sudoku solver -

i trying implement iterative sudoku solver. avoid recursion used stack, i'm having problems management. starting board represented string array (variable 'input' in following code) in each element composed of 3 numbers: [row, col] , value (i.e, "006" means element in 1st line , 1st col 6) , translated array of int constructor. when run it, cannot solution, there mistakes in nested cycles. appreciated.

import java.util.arraylist;  public class sudokusolver {      private int[][] matrix = new int[9][9];     private string[] input = { "006", "073", "102", "131", "149", "217",         "235", "303", "345", "361", "378", "422", "465", "514", "521",         "548", "582", "658", "679", "743", "752", "784", "818", "883" };      private arraylist<int[][]> stack = new arraylist<>();      public sudokusolver() {         // building board based on input array         (int n = 0; n < input.length; ++n) {             int = integer.parseint(input[n].substring(0, 1));             int j = integer.parseint(input[n].substring(1, 2));             int val = integer.parseint(input[n].substring(2, 3));             matrix[i][j] = val;         }         stack.add(matrix);     }      private boolean issolution(int[][] cells) {         (int = 0; < 9; i++) {             (int j = 0; j < 9; j++) {                 if(cells[i][j] == 0)                     return false;             }         }         return true;     }      private boolean isvalid(int i, int j, int val, int[][] cells) {         (int k = 0; k < 9; k++)             if (val == cells[k][j])                 return false;         (int k = 0; k < 9; k++)             if (val == cells[i][k])                 return false;         return true;     }      private boolean iterativesudokusolver() {         int[][] current = null;          while(stack.size() > 0 && !issolution(stack.get(0))) {             current = stack.remove(0);              (int row = 0; row < 9; row++) {                 (int col = 0; col < 9; col++) {                     if (current[row][col] == 0) {                         (int val = 1; val <= 9; val++) {                             if (isvalid(row, col, val, current)) {                                 current[row][col] = val;                                 stack.add(0, current);                                 break;                             }                         }                     }                 }             }         }         if (current != null && issolution(current))             return true;         else             return false;     }      public static void main(string [] args) {         sudokusolver sudokusolver = new sudokusolver();         boolean result = sudokusolver.iterativesudokusolver();          if (result)             system.out.println("sudoku solved");         else             system.out.println("sudoku not solved");     } } 

1. a stack implementation adding , removing 0-th element of arraylist bad idea: forces whole content of array shifted forth every time. use linkedlist or modify end of list.
2. when add , remove same instance of matrix , forth stack, still same matrix object, though may call "current" or other name. means when change in matrix , remove stack, change stays there (and in every other element of stack, identical links same object). logic of solution looks needs store previous state of solution on stack, if - allocate new array every time , copy data (also not efficient, try starting there).
3. a question has specific. "why doesn't work?" bad question. fix obvious problems first, debug, , if puzzled provide more information state of program (data in, data on step #1...n, example)