JavaAn2 — Java Exercises, Year II

A small workspace repository from the second-year Java course. It contains one complete algorithmic exercise, the eight queens problem, solved by backtracking.

Author	Ștefan Horia-Eusebiu
Language	Java 17 (Maven project, no external dependencies)
Year	2024

The eight queens problem

OptRegine.java places eight queens on a chessboard so that none of them attacks any other. The board is an int[8][8] matrix and the search proceeds column by column:

private boolean plaseazaRegine(int[][] tabla, int coloana) {
    if (coloana >= N) return true;              // all columns filled → solution found
    for (int i = 0; i < N; i++) {
        if (esteSigur(tabla, i, coloana)) {
            tabla[i][coloana] = 1;              // place
            if (plaseazaRegine(tabla, coloana + 1)) return true;
            tabla[i][coloana] = 0;              // backtrack
        }
    }
    return false;
}

Because exactly one queen is placed per column, esteSigur() only has to check three directions to the left — the row, the upper-left diagonal and the lower-left diagonal. Everything to the right is still empty, so it needs no checking at all. That observation is what keeps the safety test at O(n) instead of O(n²).

The solution is printed as a text board, with R for a queen and . for an empty square.

Known issue: in afiseazaTabla(), a queen prints as "R" while an empty square prints as ". ", so the columns do not line up. Printing "R " fixes the alignment.

Running it

mvn compile
mvn exec:java -Dexec.mainClass="javaAn2.OptRegine"

Or open the project in IntelliJ IDEA and run OptRegine directly.

Main.java is the default class generated by the IDE and simply prints a greeting followed by the numbers 1 to 5; it is not part of the exercise.

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Academic work published for portfolio purposes.