Merge pull request #1964 from TheAlgorithms/infix2posfix

Infix2posfix

.github/workflows/checkstyle.yml

@@ -20,6 +20,7 @@ jobs:
       - name: Commit Format changes
         if: failure()
         run: |
+          git diff
           git config --global user.name github-actions
           git config --global user.email '${GITHUB_ACTOR}@users.noreply.github.com'
           git remote set-url origin https://x-access-token:${{ secrets.GITHUB_TOKEN }}@github.com/$GITHUB_REPOSITORY

DIRECTORY.md

@@ -75,6 +75,7 @@
   * Stacks
     * [BalancedBrackets](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Stacks/BalancedBrackets.java)
     * [DecimalToAnyUsingStack](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Stacks/DecimalToAnyUsingStack.java)
+    * [InfixToPostfix](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Stacks/InfixToPostfix.java)
     * [NodeStack](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Stacks/NodeStack.java)
     * [StackArray](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Stacks/StackArray.java)
     * [StackArrayList](https://github.com/TheAlgorithms/Java/blob/master/DataStructures/Stacks/StackArrayList.java)

DataStructures/Stacks/InfixToPostfix.java

+package DataStructures.Stacks;
+
+import java.util.Stack;
+
+public class InfixToPostfix {
+  public static void main(String[] args) throws Exception {
+    assert "32+".equals(infix2PostFix("3+2"));
+    assert "123++".equals(infix2PostFix("1+(2+3)"));
+    assert "34+5*6-".equals(infix2PostFix("(3+4)*5-6"));
+  }
+
+  public static String infix2PostFix(String infixExpression) throws Exception {
+    if (!BalancedBrackets.isBalanced(infixExpression)) {
+      throw new Exception("invalid expression");
+    }
+    StringBuilder output = new StringBuilder();
+    Stack<Character> stack = new Stack<>();
+    for (char element : infixExpression.toCharArray()) {
+      if (Character.isLetterOrDigit(element)) {
+        output.append(element);
+      } else if (element == '(') {
+        stack.push(element);
+      } else if (element == ')') {
+        while (!stack.isEmpty() && stack.peek() != '(') {
+          output.append(stack.pop());
+        }
+        stack.pop();
+      } else {
+        while (!stack.isEmpty() && precedence(element) <= precedence(stack.peek())) {
+          output.append(stack.pop());
+        }
+        stack.push(element);
+      }
+    }
+    while (!stack.isEmpty()) {
+      output.append(stack.pop());
+    }
+    return output.toString();
+  }
+
+  private static int precedence(char operator) {
+    switch (operator) {
+      case '+':
+      case '-':
+        return 0;
+      case '*':
+      case '/':
+        return 1;
+      case '^':
+        return 2;
+      default:
+        return -1;
+    }
+  }
+}