Data commit

Task/Balanced-brackets/Java/balanced-brackets-1.java

@@ -0,0 +1,49 @@
+public class BalancedBrackets {
+
+    public static boolean hasBalancedBrackets(String str) {
+        int brackets = 0;
+        for (char ch : str.toCharArray()) {
+            if (ch == '[') {
+                brackets++;
+            } else if (ch == ']') {
+                brackets--;
+            } else {
+                return false;   // non-bracket chars
+            }
+            if (brackets < 0) {   // closing bracket before opening bracket
+                return false;
+            }
+        }
+        return brackets == 0;
+    }
+
+    public static String generateBalancedBrackets(int n) {
+        assert n % 2 == 0;   // if n is odd we can't match brackets
+        char[] ans = new char[n];
+        int openBracketsLeft = n / 2;
+        int unclosed = 0;
+        for (int i = 0; i < n; i++) {
+            if (Math.random() >= 0.5 && openBracketsLeft > 0 || unclosed == 0) {
+                ans[i] = '[';
+                openBracketsLeft--;
+                unclosed++;
+            } else {
+                ans[i] = ']';
+                unclosed--;
+            }
+        }
+        return String.valueOf(ans);
+    }
+
+    public static void main(String[] args) {
+        for (int i = 0; i <= 16; i += 2) {
+            String brackets = generateBalancedBrackets(i);
+            System.out.println(brackets + ": " + hasBalancedBrackets(brackets));
+        }
+
+        String[] tests = {"", "[]", "][", "[][]", "][][", "[[][]]", "[]][[]"};
+        for (String test : tests) {
+            System.out.println(test + ": " + hasBalancedBrackets(test));
+        }
+    }
+}

Task/Balanced-brackets/Java/balanced-brackets-2.java

@@ -0,0 +1,64 @@
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+public class BalancedBrackets {
+	
+	public static boolean areSquareBracketsBalanced(String expr) {
+		return isBalanced(expr, "", "", "[", "]", false);
+	}
+	public static boolean areBracketsBalanced(String expr) {
+		return isBalanced(expr, "", "", "{([", "})]", false);
+	}
+	public static boolean areStringAndBracketsBalanced(String expr) {
+		return isBalanced(expr, "'\"", "\\\\", "{([", "})]", true);
+	}
+	public static boolean isBalanced(String expr, String lit, String esc, String obr, String cbr, boolean other) {
+		boolean[] inLit = new boolean[lit.length()];
+		Deque<Character> stack = new ArrayDeque<Character>();
+		for (int i=0; i<expr.length(); i+=1) {
+			char c = get(expr, i);
+			int x;
+			if ((x = indexOf(inLit, true)) != -1) {
+				if (c == get(lit, x) && get(expr, i-1) != get(esc, x)) inLit[x] = false;
+			}
+			else if ((x = indexOf(lit, c)) != -1)
+				inLit[x] = true;
+			else if ((x = indexOf(obr, c)) != -1)
+				stack.push(get(cbr, x));
+			else if (indexOf(cbr, c) != -1) {
+				if (stack.isEmpty() || stack.pop() != c) return false;
+			}
+			else if (!other)
+				return false;
+		}
+		return stack.isEmpty();
+	}
+	
+	static int indexOf(boolean[] a, boolean b) {
+		for (int i=0; i<a.length; i+=1) if (a[i] == b) return i;
+		return -1;
+	}
+	static int indexOf(String s, char c) {
+		return s.indexOf(c);
+	}
+	static char get(String s, int i) {
+		return s.charAt(i);
+	}
+
+	public static void main(String[] args) {
+		System.out.println("With areSquareBracketsBalanced:");
+		for (String s: new String[] {
+				"", "[]", "[][]", "[[][]]", "][", "][][", "[]][[]", "[", "]"
+			}
+		) {
+			System.out.printf("%s: %s\n", s, areSquareBracketsBalanced(s));
+		}
+		System.out.println("\nBut also with areStringAndBracketsBalanced:");
+		for (String s: new String[] {
+				"x[]", "[x]", "[]x", "([{}])", "([{}]()", "([{ '([{\\'([{' \"([{\\\"([{\" }])",
+			}
+		) {
+			System.out.printf("%s: %s\n", s, areStringAndBracketsBalanced(s));
+		}
+	}
+}

Task/Balanced-brackets/Java/balanced-brackets.java

@@ -0,0 +1,19 @@
+grammar balancedBrackets ;
+
+options {
+	language = Java;
+}
+
+bb	:	{System.out.print("input is: ");} (balancedBrackets {System.out.print($balancedBrackets.text);})* NEWLINE {System.out.println();}
+	;
+balancedBrackets
+	:	OpenBracket balancedBrackets* CloseBracket
+	;
+OpenBracket
+	:	'['
+	;
+CloseBracket
+	:	']'
+	;
+NEWLINE	:	'\r'? '\n'
+	;