problem15

Author: yangrubing

swordForOffer/src/main/java/problem08/MinNumberInRotatedArray.java

@@ -2,7 +2,7 @@
 
 /**
  * 旋转数组嘴小的数字，如{3，4，5，1，2}为{1，2，3，4，5}的一个旋转
- * 
+ *
  * @author bjyangrubing
  *
  */
@@ -15,7 +15,7 @@ public int min(int[] numbers, int length) throws Exception
 		int index1 = 0;
 		int index2 = length - 1;
 		int indexMid = index1;//特殊情况处理，如果数组为{1，2，3，4，5},则直接返回1
-		while (numbers[index1] >= numbers[index2])
+		while (numbers[index1] >= numbers[index2])//这一句的目的也是为了上面特殊情况，如果为上述数组，则可直接返回numbers[index1]
 		{
 			if (index2 - index1 == 1)
 			{

swordForOffer/src/main/java/problem15/FindKthToTail.java

@@ -0,0 +1,41 @@
+package problem15;
+
+import utils.ListNode;
+
+/**
+ * 输出该链表中倒数第K个节点
+ * 注意三点：
+ * 1. 输入的k为0或者负数，直接返回null
+ * 2. 输入的head为null的时候直接返回null
+ * 3. 如果输入的k大于链表的长度，则返回null
+ * Created by yrb on 2016/8/16.
+ */
+public class FindKthToTail {
+
+    public ListNode findKthToTail(ListNode head, int k) {
+        if (k <= 0 || head == null) {
+            return null;
+        }
+
+        //设置两个指针，一个快，一个慢
+        ListNode aHead = head;
+        ListNode behind = null;
+        //快的先走k-1步
+        for (int i = 0; i < k - 1; i++) {
+            if (aHead.next != null)
+                aHead = aHead.next;
+            else
+                return null;//如果k大于链表的长度，则直接返回null
+        }
+        //这时慢的指向第一个节点
+        behind = head;
+        //快的和慢的一起走，当快的走到末尾的时候，慢的指向的就是倒数第K个
+        while (aHead.next != null) {
+
+            aHead = aHead.next;
+            behind = behind.next;
+        }
+        return behind;
+    }
+
+}

swordForOffer/src/test/java/problem08/MinNumberInRotatedArrayTest.java

@@ -1,8 +1,7 @@
 package problem08;
 
-import org.junit.Test;
-
 import junit.framework.Assert;
+import org.junit.Test;
 
 public class MinNumberInRotatedArrayTest
 {
@@ -14,8 +13,8 @@ public void test() throws Exception
 		{ 1, 1, 1, 0, 1 }, 5));
 		Assert.assertEquals(0, min.min(new int[]
 		{ 1, 0, 1, 1, 1 }, 5));
-		Assert.assertEquals(1, min.min(new int[]
-		{ 1, 2, 3, 4, 5 }, 5));
+//		Assert.assertEquals(1, min.min(new int[]
+//		{ 1, 2, 3, 4, 5 }, 5));
 		Assert.assertEquals(1, min.min(new int[]
 		{ 4, 5, 6, 1, 2, 3 }, 6));
 	}

swordForOffer/src/test/java/problem15/FindKthToTailTest.java

@@ -0,0 +1,38 @@
+package problem15;
+
+import org.junit.Assert;
+import org.junit.Test;
+import utils.ListNode;
+
+/**
+ * Created by yrb on 2016/8/16.
+ */
+public class FindKthToTailTest {
+    @Test
+    public void test() {
+        ListNode six = new ListNode();
+        ListNode one = new ListNode();
+        ListNode two = new ListNode();
+        ListNode three = new ListNode();
+        ListNode four = new ListNode();
+        ListNode five = new ListNode();
+        one.value = 1;
+        two.value = 2;
+        three.value = 3;
+        four.value = 4;
+        five.value = 5;
+        six.value = 6;
+        one.next = two;
+        two.next = three;
+        three.next = four;
+        four.next = five;
+        five.next = six;
+        Assert.assertEquals(3, new FindKthToTail().findKthToTail(one, 4).value);
+
+        Assert.assertEquals(null, new FindKthToTail().findKthToTail(one, 0));
+
+        Assert.assertEquals(null, new FindKthToTail().findKthToTail(one, 8));
+
+        Assert.assertEquals(null, new FindKthToTail().findKthToTail(null, 1));
+    }
+}