Merge pull request codemistic#614 from tiger3768/stjava

Add : Balanced Brackets and InfixToPrefix program in Java

Author: gantavyamalviya

Java/Stack/BalancedBrackets.java

@@ -0,0 +1,32 @@
+//Program to check for Balanced Brackets in Java
+
+import java.util.Stack;
+
+public class BalancedBrackets {
+ public static boolean isBalanced(String expression) {
+ Stack<Character> bracketStack = new Stack<>();
+ int n = expression.length();
+ for(int i = 0 ; i < n ; i++){
+ char bracket = expression.charAt(i);
+ if(isNotB(bracket)) continue;
+ if(isOpeningB(bracket)) bracketStack.push(bracket);
+ else{
+ if(!bracketStack.isEmpty() && validOpeningB(bracket) != bracketStack.peek()) return false;
+ else bracketStack.pop();
+ }
+ }
+ return bracketStack.isEmpty();
+ }
+ static boolean isNotB(char bracket){
+ return !("(){}[]".contains(bracket + ""));
+ }
+ static boolean isOpeningB(char bracket){
+ return "({[".contains(bracket + "");
+ }
+ static char validOpeningB(char bracket){
+ if(bracket == ')') return '(';
+ if(bracket == '}') return '{';
+ if(bracket == ']') return '[';
+ return '\0';
+ }
+}

Java/Stack/InfixToPrefix.java

@@ -0,0 +1,42 @@
+//Java Program to convert Infix Expression to Prefix
+import java.util.Stack;
+
+public class InfixToPrefix {
+ public static void main(String[] args) {
+ System.out.println("1+2+3 -> " + infix2Prefix("1+2+3"));
+ System.out.println("A^B-(C+D) -> " + infix2Prefix("A^B-(C+D)"));
+ System.out.println("(P/L+(F*J) -> " + infix2Prefix("(P/L+(F*J)"));
+ }
+ public static String infix2Prefix(String expression){
+ if(!BalancedBrackets.isBalanced(expression)) return "Invalid Expression";
+ Stack<Character> operatorStack = new Stack<>();
+ StringBuilder prefixExpression = new StringBuilder();
+ int n = expression.length();
+ for(int i = n - 1 ; i >= 0 ; i--){
+ char scanned = expression.charAt(i);
+ if(Character.isLetterOrDigit(scanned)) prefixExpression.append(scanned);
+ else if(scanned == ')') operatorStack.push(scanned);
+ else if(scanned == '('){
+ while(!operatorStack.isEmpty() && operatorStack.peek() != ')'){
+ prefixExpression.append(operatorStack.pop());
+ }
+ if(!operatorStack.isEmpty()) operatorStack.pop();
+ }
+ else if(operatorStack.isEmpty() || operatorStack.peek() == ')') operatorStack.push(scanned);
+ else{
+ while(!operatorStack.isEmpty() && precedence(operatorStack.peek()) < precedence(scanned)){
+ prefixExpression.append(operatorStack.pop());
+ }
+ operatorStack.push(scanned);
+ }
+ }
+ while(!operatorStack.isEmpty()) prefixExpression.append(operatorStack.pop());
+ return prefixExpression.reverse().toString();
+ }
+ static int precedence(char operator){
+ if(operator == '^') return 3;
+ if(operator == '*' || operator == '/') return 2;
+ if(operator == '+' || operator == '-') return 1;
+ return 0;
+ }
+}