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11 changes: 7 additions & 4 deletions src/main/java/com/thealgorithms/backtracking/NQueens.java
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.logging.Logger;

/**
* Problem statement: Given a N x N chess board. Return all arrangements in
Expand Down Expand Up @@ -41,6 +42,8 @@
*/
public final class NQueens {

private static final Logger LOGGER = Logger.getLogger(NQueens.class.getName());

// Store occupied rows for constant time safety check
private static final Set<Integer> OCROWS = new HashSet<>();

Expand All @@ -63,13 +66,13 @@ public static void placeQueens(final int queens) {
List<List<String>> arrangements = new ArrayList<>();
getSolution(queens, arrangements, new int[queens], 0);
if (arrangements.isEmpty()) {
System.out.println(" no way to place " + queens + " queens on board of size " + queens + "x" + queens);
LOGGER.info(" no way to place " + queens + " queens on board of size " + queens + "x" + queens);
} else {
System.out.println("Arrangement for placing " + queens + " queens");
LOGGER.info("Arrangement for placing " + queens + " queens");
}
for (List<String> arrangement : arrangements) {
arrangement.forEach(System.out::println);
System.out.println();
arrangement.forEach(row -> LOGGER.info(row));
LOGGER.info("");
}
}

Expand Down
24 changes: 12 additions & 12 deletions src/main/java/com/thealgorithms/stacks/StackPostfixNotation.java
Original file line number Diff line number Diff line change
@@ -1,7 +1,8 @@
package com.thealgorithms.stacks;

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;
import java.util.Stack;
import java.util.function.BiFunction;

/**
Expand Down Expand Up @@ -35,24 +36,23 @@ private static BiFunction<Integer, Integer, Integer> getOperator(final String op
}
}

private static void performOperation(Stack<Integer> s, final String operationSymbol) {
private static void performOperation(Deque<Integer> s, final String operationSymbol) {
if (s.size() < 2) {
throw new IllegalArgumentException("exp is not a proper postfix expression (too few arguments).");
}
s.push(getOperator(operationSymbol).apply(s.pop(), s.pop()));
}

private static void consumeExpression(Stack<Integer> s, final String exp) {
Scanner tokens = new Scanner(exp);

while (tokens.hasNext()) {
if (tokens.hasNextInt()) {
s.push(tokens.nextInt());
} else {
performOperation(s, tokens.next());
private static void consumeExpression(Deque<Integer> s, final String exp) {
try (Scanner tokens = new Scanner(exp)) {
while (tokens.hasNext()) {
if (tokens.hasNextInt()) {
s.push(tokens.nextInt());
} else {
performOperation(s, tokens.next());
}
}
}
tokens.close();
}

/**
Expand All @@ -62,7 +62,7 @@ private static void consumeExpression(Stack<Integer> s, final String exp) {
* @exception IllegalArgumentException exp is not a valid postix expression.
*/
public static int postfixEvaluate(final String exp) {
Stack<Integer> s = new Stack<>();
Deque<Integer> s = new ArrayDeque<>();
consumeExpression(s, exp);
if (s.size() != 1) {
throw new IllegalArgumentException("exp is not a proper postfix expression.");
Expand Down
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