数独解算器不更改值

Question

I am trying to implement a sudoku solver that works on any square sized board (4x4, 9x9, 16x6 etc.) This is what i currently have for my algorithm but once it runs no values end up being changed and theGrid is the same as before the solve was run.
I really don't know where it has gone wrong and any help is appreciated.

 private int[][] theGrid;
 private int emptyValue = -1;

 public int[][] solve() {
    recSolve(0, 0);
    return theGrid;
 }


 void recSolve(int i, int j) {
    int size = theGrid.length;
    if (i == size) {
        i = 0;
        if (++j == size)
            return;
            //done
    }
    if (theGrid[i][j] != emptyValue)  // skip filled cells
        recSolve(i+1,j);

    for (int val = 1; val <= size; ++val) {
        if (!isPresent(theGrid, i, j, val)) {
            theGrid[i][j] = val;
            recSolve(i+1,j)
        }
    }
    theGrid[i][j] = emptyValue; // reset on backtrack
}

 boolean isPresent(int[][] grid, int row, int col, int num){
    for(int i = 0; i < theGrid.length; i++){
        if(theGrid[i][col] == num) return false;
        if(theGrid[row][i] == num) return false;
    }
    int side = (int)Math.sqrt(theGrid.length);

    int rowStart = row - row % side;
    int colStart = col - col % side;

    for(int m = 0; m < side; m++){
        for(int k = 0; k < side; k++){
            if(grid[rowStart + k][colStart + m] == num) return false;
        }
    }
    return true;
}

Answer 1

I'd recommend running through a debugger and you'll soon see what's wrong. As a start, isPresent returns true when the value is not present, which is the opposite of what I'd expect.