N-Queens in Java using Stacks, Keeps taking the same route after backtracking -

title pretty says all. i've been working on , can't figure out way prevent happening. perhaps way store invalid placements? or how implement way 'resume' last time @ row doesn't pick same value again?

ignore while i, debugging. same prints.

import java.util.stack;  public class nqueens {  //***** fill in code here ***** //feel free add additional methods necessary  //finds , prints out solutions n-queens problem public static int solve(int n) {     //***** fill in code here *****     //scaffolding code stacks.pdf     //------------------------------------------------------------------------------------------------------------------     //  create empty stack , set current position 0     stack<integer> s = new stack<integer>();      int column = 0;     int row = 0;      int solutionscount = 0;     int = 0;     //repeat {     //loop current position last position until valid position found //current row     while (i < 5){          for(column = 0; column < n ;column++) {             //if there valid position             system.out.println("top of loop");             system.out.println("column/index = " + column + "; row is: " + row);             system.out.println("stack size = " + s.size());             system.out.println();             if (isvalid(s, column, row)) {                 s.push(column);                 //push position stack, set current position 0 // move next ro                 row++;                 column = 0;             }//if         }//for          //if there no valid position         if(!isvalid(s, column, row) || column >= n){             //if stack empty, break // stop search             if(s.size() == 0){                 break; //stop search             }//if             //else pop stack, set current position next position // backtracking previous row             else{                 s.pop();                 column++;                 row--;             }//else         }//if          //if stack has size n { // solution found         if (s.size() == n){             solutionscount++;             printsolution(s);             //pop stack, set current position next position // backtracking find next solution             s.pop();             row--;             column++;         }//if          else {         }//else     i++;     // make sure change when not bug testing 4x4     }//end loop //update following statement return number of solutions found return solutionscount;  }//solve() 

this looks homework, here pointers:

1. you modifying column variable after for loop. obviously, intend value carry on next iteration of while. first thing when while starts again set column 0 for (column = 0; ....), overrides value. information column supposed carry 1 iteration of while next?
2. you setting column 0 inside for loop incremented 1 column++ before next for iteration.
3. you using column in if statement after loop. expect value of variable after for loop completes?
4. after for loop have 2 if statements trying check same condition -- whether for loop found solution. second if clearer it. need both ifs?
5. you putting column values stack, when pop them off stack, discard them. don't have use these values?