From 656bbf8fb3300f7eabb6be4f9af594499f9bdd71 Mon Sep 17 00:00:00 2001 From: johnChnia Date: Mon, 10 Apr 2017 02:11:00 +0800 Subject: [PATCH] =?UTF-8?q?=E5=AE=8C=E6=88=90stackutil?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- .../coding2017/basic/{ => stack}/Stack.java | 2 +- .../coding2017/basic/stack/StackUtil.java | 122 ++++++++++++++++++ .../johnChnia/coding2017/basic/StackTest.java | 1 + .../coding2017/basic/stack/StackUtilTest.java | 66 ++++++++++ 4 files changed, 190 insertions(+), 1 deletion(-) rename group24/315863321/src/main/java/com/johnChnia/coding2017/basic/{ => stack}/Stack.java (97%) create mode 100644 group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/StackUtil.java create mode 100644 group24/315863321/src/test/java/com/johnChnia/coding2017/basic/stack/StackUtilTest.java diff --git a/group24/315863321/src/main/java/com/johnChnia/coding2017/basic/Stack.java b/group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/Stack.java similarity index 97% rename from group24/315863321/src/main/java/com/johnChnia/coding2017/basic/Stack.java rename to group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/Stack.java index 3ddab60493..c8f1ce7d15 100644 --- a/group24/315863321/src/main/java/com/johnChnia/coding2017/basic/Stack.java +++ b/group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/Stack.java @@ -1,4 +1,4 @@ -package com.johnChnia.coding2017.basic; +package com.johnChnia.coding2017.basic.stack; import com.johnChnia.coding2017.basic.linklist.LinkedList; diff --git a/group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/StackUtil.java b/group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/StackUtil.java new file mode 100644 index 0000000000..4b7c4687d7 --- /dev/null +++ b/group24/315863321/src/main/java/com/johnChnia/coding2017/basic/stack/StackUtil.java @@ -0,0 +1,122 @@ +package com.johnChnia.coding2017.basic.stack; + +/** + * Created by john on 2017/4/7. + */ +public class StackUtil { + + + /** + * 假设栈中的元素是Integer, 从栈顶到栈底是 : 5,4,3,2,1 调用该方法后， 元素次序变为: 1,2,3,4,5 + * 注意：只能使用Stack的基本操作，即push,pop,peek,isEmpty， 可以使用另外一个栈来辅助 + */ + public static void reverse(Stack s) { + if (s.empty()) { + return; + } + E item = s.pop(); + reverse(s); + insertAtBottom(item, s); + } + + /** + * @param item 插入底部的元素 + * @param s 栈对象引用 + */ + private static void insertAtBottom(E item, Stack s) { + if (s.empty()) { + s.push(item); + } else { + E temp = s.pop(); + insertAtBottom(item, s); + s.push(temp); + } + } + + + /** + * 删除栈中的某个元素 注意：只能使用Stack的基本操作，即push,pop,peek,isEmpty， 可以使用另外一个栈来辅助 + * + * @param o + */ + public static void remove(Stack s, Object o) { + if (s.empty()) { + return; + } + E item = s.pop(); + if (!o.equals(item)) { //没有考虑o为null的情况 + remove(s, o); + s.push(item); + } + } + + /** + * 从栈顶取得len个元素, 原来的栈中元素保持不变 + * 注意：只能使用Stack的基本操作，即push,pop,peek,isEmpty， 可以使用另外一个栈来辅助 + * + * @param len + * @return + */ + public static Object[] getTop(Stack s, int len) { + if (len > s.size()) { + throw new IllegalArgumentException("Len: " + len + ", Size" + s.size()); + } + Object[] array = new Object[len]; + int index = 0; + getArray(s, array, index); + return array; + } + + /** + * 采用递归的方式把len个元素加到数组中，且保持原栈中元素不变。 + * + * @param s 栈 + * @param array Object数组 + * @param index 数组索引 + */ + private static void getArray(Stack s, Object[] array, int index) { + if (s.empty() || index == array.length) { + return; + } + E item = s.pop(); + array[index++] = item; + getArray(s, array, index); + s.push(item); + } + + /** + * 字符串s 可能包含这些字符： ( ) [ ] { }, a,b,c... x,yz + * 使用堆栈检查字符串s中的括号是不是成对出现的。 + * 例如s = "([e{d}f])" , 则该字符串中的括号是成对出现， 该方法返回true + * 如果 s = "([b{x]y})", 则该字符串中的括号不是成对出现的， 该方法返回false; + * + * @param s + * @return + */ + public static boolean isValidPairs(String s) { // last unclosed first closed + Stack stack = new Stack<>(); + for (int i = 0; i < s.length(); i++) { + String subStr = s.substring(i, i + 1); + if ("([{".contains(subStr)) { + stack.push(subStr); + } else if (")]}".contains(subStr)) { + if (stack.empty()) { + return false; + } + String left = stack.pop(); + if (subStr.equals(")")) { + if(!left.equals("(")) + return false; + }else if(subStr.equals("]")){ + if(!left.equals("[")) + return false; + }else if(subStr.equals("}")){ + if(!left.equals("{")) + return false; + } + } + } + return stack.empty(); + } + +} \ No newline at end of file diff --git a/group24/315863321/src/test/java/com/johnChnia/coding2017/basic/StackTest.java b/group24/315863321/src/test/java/com/johnChnia/coding2017/basic/StackTest.java index 9d84f7367a..c6f4ec1b2c 100644 --- a/group24/315863321/src/test/java/com/johnChnia/coding2017/basic/StackTest.java +++ b/group24/315863321/src/test/java/com/johnChnia/coding2017/basic/StackTest.java @@ -1,5 +1,6 @@ package com.johnChnia.coding2017.basic; +import com.johnChnia.coding2017.basic.stack.Stack; import org.junit.Before; import org.junit.Test; diff --git a/group24/315863321/src/test/java/com/johnChnia/coding2017/basic/stack/StackUtilTest.java b/group24/315863321/src/test/java/com/johnChnia/coding2017/basic/stack/StackUtilTest.java new file mode 100644 index 0000000000..0a2f277d49 --- /dev/null +++ b/group24/315863321/src/test/java/com/johnChnia/coding2017/basic/stack/StackUtilTest.java @@ -0,0 +1,66 @@ +package com.johnChnia.coding2017.basic.stack; + +import org.junit.Assert; +import org.junit.Before; +import org.junit.Test; + +import static com.johnChnia.coding2017.basic.stack.StackUtil.*; + + +/** + * Created by john on 2017/4/7. + */ +public class StackUtilTest { + + Stack s1; + Stack s2; + Stack s3; + + @Before + public void setUp() throws Exception { + s1 = new Stack<>(); + s2 = new Stack<>(); + s3 = new Stack<>(); + + } + + @Test + public void testReverse() throws Exception { + for (int i = 0; i < 4; i++) { + s1.push(i); + } + reverse(s1); + Assert.assertEquals("0→1→2→3", s1.toString()); + } + + @Test + public void testRemove() throws Exception { + for (int i = 0; i < 4; i++) { + s2.push(i); + } + remove(s2, 1); + Assert.assertEquals("3→2→0", s2.toString()); + } + + @Test + public void testGetTop() throws Exception { + for (int i = 0; i < 4; i++) { + s3.push(i); + } + Object[] array = getTop(s3, 2); + Assert.assertEquals(array.length, 2); + Assert.assertEquals(array[0], 3); + Assert.assertEquals(array[1], 2); + Assert.assertEquals("3→2→1→0", s3.toString()); + + } + + @Test + public void testIsValidPairs() throws Exception { + String s1 = "([e{d}f])"; + Assert.assertTrue(isValidPairs(s1)); + String s2 = "([b{x]y})"; + Assert.assertFalse(isValidPairs(s2)); + } + +} \ No newline at end of file