Data update

Task/Parsing-Shunting-yard-algorithm/Dart/parsing-shunting-yard-algorithm.dart

@@ -0,0 +1,84 @@
+import 'dart:collection';
+
+class ShuntingYard {
+  static final Map<String, OperatorInfo> operators = {
+    '^': OperatorInfo('^', 4, true),
+    '*': OperatorInfo('*', 3, false),
+    '/': OperatorInfo('/', 3, false),
+    '+': OperatorInfo('+', 2, false),
+    '-': OperatorInfo('-', 2, false),
+  };
+
+  static String toPostfix(String infix) {
+    List<String> tokens = infix.split(' ');
+    Queue<String> stack = Queue<String>();
+    List<String> output = [];
+
+    void printState(String action) {
+      List<String> stackList = stack.toList();
+      stackList = stackList.reversed.toList();
+      print('${(action + ":").padRight(4)} ${"stack[ ${stackList.join(" ")} ]".padRight(18)} out[ ${output.join(" ")} ]');
+    }
+
+    for (String token in tokens) {
+      if (isNumeric(token)) {
+        output.add(token);
+        printState(token);
+      } else if (operators.containsKey(token)) {
+        OperatorInfo op1 = operators[token]!;
+        while (stack.isNotEmpty && operators.containsKey(stack.last)) {
+          OperatorInfo op2 = operators[stack.last]!;
+          int c = op1.precedence.compareTo(op2.precedence);
+          if (c < 0 || (!op1.rightAssociative && c <= 0)) {
+            output.add(stack.removeLast());
+          } else {
+            break;
+          }
+        }
+        stack.add(token);
+        printState(token);
+      } else if (token == "(") {
+        stack.add(token);
+        printState(token);
+      } else if (token == ")") {
+        String top = "";
+        while (stack.isNotEmpty && (top = stack.removeLast()) != "(") {
+          output.add(top);
+        }
+        if (top != "(") throw ArgumentError("No matching left parenthesis.");
+        printState(token);
+      }
+    }
+
+    while (stack.isNotEmpty) {
+      String top = stack.removeLast();
+      if (!operators.containsKey(top)) throw ArgumentError("No matching right parenthesis.");
+      output.add(top);
+    }
+    printState("pop");
+
+    return output.join(" ");
+  }
+
+  static bool isNumeric(String str) {
+    try {
+      int.parse(str);
+      return true;
+    } catch (e) {
+      return false;
+    }
+  }
+}
+
+class OperatorInfo {
+  final String symbol;
+  final int precedence;
+  final bool rightAssociative;
+
+  OperatorInfo(this.symbol, this.precedence, this.rightAssociative);
+}
+
+void main() {
+  String infix = "3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3";
+  print(ShuntingYard.toPostfix(infix));
+}