完成中序、前序、后序表达式

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/InfixExpr.java

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+package com.johnChnia.coding2017.basic.stack.expr;
+
+
+import com.johnChnia.coding2017.basic.List;
+
+public class InfixExpr {
+	String expr = null;
+
+	public InfixExpr(String expr) {
+		this.expr = expr;
+	}
+
+	public float evaluate() {
+		List<Token> tokens = InfixToPostfix.convert(this.expr);
+		return PostfixExpr.evaluate(tokens);
+	}
+
+
+}

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/InfixExprTest.java

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+package com.johnChnia.coding2017.basic.stack.expr;
+
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+
+public class InfixExprTest {
+
+	@Before
+	public void setUp() throws Exception {
+	}
+
+	@After
+	public void tearDown() throws Exception {
+	}
+
+	@Test
+	public void testEvaluate() {
+		//InfixExpr expr = new InfixExpr("300*20+12*5-20/4");
+		{
+			InfixExpr expr = new InfixExpr("2+3*4+5");
+			Assert.assertEquals(19.0, expr.evaluate(), 0.001f);
+		}
+		{
+			InfixExpr expr = new InfixExpr("3*20+12*5-40/2");
+			Assert.assertEquals(100.0, expr.evaluate(), 0.001f);
+		}
+
+		{
+			InfixExpr expr = new InfixExpr("3*20/2");
+			Assert.assertEquals(30, expr.evaluate(), 0.001f);
+		}
+
+		{
+			InfixExpr expr = new InfixExpr("20/2*3");
+			Assert.assertEquals(30, expr.evaluate(), 0.001f);
+		}
+
+		{
+			InfixExpr expr = new InfixExpr("10-30+50");
+			Assert.assertEquals(30, expr.evaluate(), 0.001f);
+		}
+		{
+			InfixExpr expr = new InfixExpr("10-2*3+50");
+			Assert.assertEquals(54, expr.evaluate(), 0.001f);
+		}
+
+	}
+
+}

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/InfixToPostfix.java

@@ -0,0 +1,37 @@
+package com.johnChnia.coding2017.basic.stack.expr;
+
+
+import com.johnChnia.coding2017.basic.ArrayList;
+import com.johnChnia.coding2017.basic.List;
+import com.johnChnia.coding2017.basic.stack.Stack;
+
+
+/***
+ * Rule:
+ */
+public class InfixToPostfix {
+
+    public static List<Token> convert(String expr) {
+        TokenParser tokenParser = new TokenParser();
+        List<Token> tokens = tokenParser.parse(expr);
+        List<Token> list = new ArrayList<>();
+        Stack<Token> stack = new Stack<>();
+        for (int i = 0; i < tokens.size(); i++) {
+            Token token = tokens.get(i);
+            if (token.isNumber()) {
+                list.add(token);
+            } else if (token.isOperator()) {
+                while (!stack.empty() && !token.hasHigherPriority(stack.peek())) {
+                        list.add(stack.pop());
+                }
+                stack.push(token);
+
+            }
+        }
+        while (!stack.empty()) {
+            list.add(stack.pop());
+        }
+        return list;
+    }
+
+}

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/Operator.java

@@ -0,0 +1,42 @@
+package com.johnChnia.coding2017.basic.stack.expr;
+
+import com.johnChnia.coding2017.basic.stack.Stack;
+
+/**
+ * Created by john on 2017/4/20.
+ */
+public class Operator {
+
+    public void handlerToken(String fix, Stack<Float> stack, Token token) {
+        if (token.isNumber()) {
+            stack.push(Float.parseFloat(token.toString()));
+        } else if (token.isOperator()) {
+            float p = stack.pop();
+            float q = stack.pop();
+            stack.push(perform(fix, token.toString(), p, q));
+        }
+    }
+
+
+    private float perform(String fix, String operator, float p, float q) {
+        float result = 0.0f;
+        if (operator.equals("+")) {
+            result = p + q;
+        } else if (operator.equals("-")) {
+            if (fix.equals("postfix")) {
+                result = q - p;
+            } else if (fix.equals("prefix")) {
+                result = p - q;
+            }
+        } else if (operator.equals("*")) {
+            result = p * q;
+        } else if (operator.equals("/")) {
+            if (fix.equals("postfix")) {
+                result = q / p;
+            } else if (fix.equals("prefix")) {
+                result = p / q;
+            }
+        }
+        return result;
+    }
+}

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/PostfixExpr.java

@@ -0,0 +1,36 @@
+package com.johnChnia.coding2017.basic.stack.expr;
+
+import com.johnChnia.coding2017.basic.List;
+import com.johnChnia.coding2017.basic.stack.Stack;
+
+public class PostfixExpr {
+    private String expr = null;
+    static Operator operator = new Operator();
+
+
+    public PostfixExpr(String expr) {
+        this.expr = expr;
+    }
+
+    public float evaluate() {
+        TokenParser tokenParser = new TokenParser();
+        List<Token> tokens = tokenParser.parse(this.expr);
+        Stack<Float> stack = new Stack<>();
+        for (int i = 0; i < tokens.size(); i++) {
+            operator.handlerToken("postfix", stack, tokens.get(i));
+
+        }
+
+        return stack.pop();
+    }
+
+    public static float evaluate(List<Token> tokens) {
+        Stack<Float> stack = new Stack<>();
+        for (int i = 0; i < tokens.size(); i++) {
+            operator.handlerToken("postfix", stack, tokens.get(i));
+        }
+        return stack.pop();
+    }
+
+
+}

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/PostfixExprTest.java

@@ -0,0 +1,41 @@
+package com.johnChnia.coding2017.basic.stack.expr;
+
+
+
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+
+
+public class PostfixExprTest {
+
+	@Before
+	public void setUp() throws Exception {
+	}
+
+	@After
+	public void tearDown() throws Exception {
+	}
+
+	@Test
+	public void testEvaluate() {
+		{
+			PostfixExpr expr = new PostfixExpr("6 5 2 3 + 8 * + 3 + *");
+			Assert.assertEquals(288, expr.evaluate(),0.0f);
+		}
+		{
+			//9+(3-1)*3+10/2
+			PostfixExpr expr = new PostfixExpr("9 3 1-3*+ 10 2/+");
+			Assert.assertEquals(20, expr.evaluate(),0.0f);
+		}
+
+		{
+			//10-2*3+50
+			PostfixExpr expr = new PostfixExpr("10 2 3 * - 50 +");
+			Assert.assertEquals(54, expr.evaluate(),0.0f);
+		}
+	}
+
+}

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/PrefixExpr.java

@@ -0,0 +1,25 @@
+package com.johnChnia.coding2017.basic.stack.expr;
+
+import com.johnChnia.coding2017.basic.List;
+import com.johnChnia.coding2017.basic.stack.Stack;
+
+public class PrefixExpr {
+    String expr = null;
+
+    public PrefixExpr(String expr) {
+        this.expr = expr;
+    }
+
+    public float evaluate() {
+        TokenParser tokenParser = new TokenParser();
+        List<Token> tokens = tokenParser.parse(this.expr);
+        Operator operator = new Operator();
+        Stack<Float> stack = new Stack<>();
+        for (int i = tokens.size() - 1; i >= 0; i--) {
+            operator.handlerToken("prefix", stack, tokens.get(i));
+        }
+        return stack.pop();
+    }
+
+
+}

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/PrefixExprTest.java

@@ -0,0 +1,45 @@
+package com.johnChnia.coding2017.basic.stack.expr;
+
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+
+public class PrefixExprTest {
+
+    @Before
+    public void setUp() throws Exception {
+    }
+
+    @After
+    public void tearDown() throws Exception {
+    }
+
+    @Test
+    public void testEvaluate() {
+        {
+            // 2*3+4*5
+            PrefixExpr expr = new PrefixExpr("+ * 2 3* 4 5");
+            Assert.assertEquals(26, expr.evaluate(), 0.001f);
+        }
+        {
+            // 4*2 + 6+9*2/3 -8
+            PrefixExpr expr = new PrefixExpr("-++6/*2 9 3 * 4 2 8");
+            Assert.assertEquals(12, expr.evaluate(), 0.001f);
+        }
+        {
+            //(3+4)*5-6
+            PrefixExpr expr = new PrefixExpr("- * + 3 4 5 6");
+            Assert.assertEquals(29, expr.evaluate(), 0.001f);
+        }
+        {
+            //1+((2+3)*4)-5
+            PrefixExpr expr = new PrefixExpr("- + 1 * + 2 3 4 5");
+            Assert.assertEquals(16, expr.evaluate(), 0.001f);
+        }
+
+
+    }
+
+}

group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/expr/Token.java

@@ -0,0 +1,50 @@
+package com.johnChnia.coding2017.basic.stack.expr;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+class Token {
+	public static final List<String> OPERATORS = Arrays.asList("+", "-", "*", "/");
+	private static final Map<String,Integer> priorities = new HashMap<>();
+	static {
+		priorities.put("+", 1);
+		priorities.put("-", 1);
+		priorities.put("*", 2);
+		priorities.put("/", 2);
+	}
+	static final int OPERATOR = 1;
+	static final int NUMBER = 2;
+	String value;
+	int type;
+	public Token(int type, String value){
+		this.type = type;
+		this.value = value;
+	}		
+
+	public boolean isNumber() {
+		return type == NUMBER;
+	}
+
+	public boolean isOperator() {
+		return type == OPERATOR;
+	}
+
+	public int getIntValue() {
+		return Integer.valueOf(value).intValue();
+	}
+	public String toString(){
+		return value;
+	}
+
+	public boolean hasHigherPriority(Token t){
+		if(!this.isOperator() && !t.isOperator()){
+			throw new RuntimeException("numbers can't compare priority");
+		}
+		return priorities.get(this.value) - priorities.get(t.value) > 0;
+	}
+
+
+
+}