This is theN-Queens problem solution with abacktraking approach, look here for theN-Queens brute force approach.

If you are not familiar with theN-Queens problemlook here for an explanation.

You can find the complete code for this post here:NQueensBacktracking.java.

The main difference from this one and the brute force approach is that we will check if a current permutation is a viable solution every time we add a queen, and if it’s not we will not continue pursuing that particular permutation:

static void findSolutions(LinkedHashSetWrapper perm, int n){    if(perm.size() == n) {        System.out.println(perm);        return;    }    for(int i = 0; i < n; i++){        if(!perm.contains(i)) {            perm.add(i);            if(isSolution(perm.copyInnerArray())){                findSolutions(perm, n);            }            perm.removeLastElement();        }    }}

In the next image you can see a solution for N = 4 (clic to enlarge)

Download the complete code from this post hereNQueensBacktracking.java.