minInRotatedArray

Author: yangrubing

swordForOffer/src/main/java/problem07/QueueWithTwoStack.java

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+package problem07;
+
+import java.util.Stack;
+
+/**
+ * 两个栈实现一个队列
+ * @author bjyangrubing
+ *
+ */
+public class QueueWithTwoStack
+{
+	/*用两个栈实现一个队列，完成两个函数appendTail和deletedHead，分别是在队列尾部插入节点和
+	在队列头部删除节点的功能*/
+	private Stack<String> stack1 = new Stack<String>();
+	private Stack<String> stack2 = new Stack<String>();
+
+	public void appendTail(String elem)
+	{
+		stack1.push(elem);
+	}
+
+	public String deletedHead() throws Exception
+	{
+		while (!stack1.isEmpty())//如果栈1不为空，则把栈1的元素全部push到栈2
+		{
+			stack2.push(stack1.pop());
+		}
+
+		if (stack2.size() == 0)
+			throw new Exception("queue is empty");
+		String head = stack2.pop();//从栈2里面出栈
+		return head;
+	}
+
+}

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

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+package problem08;
+
+/**
+ * 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
+ *
+ */
+public class MinNumberInRotatedArray
+{
+	public int min(int[] numbers, int length) throws Exception
+	{
+		if (numbers == null || length <= 0)//边界条件判断
+			throw new Exception("Invalid parameters.");
+		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])
+		{
+			if (index2 - index1 == 1)
+			{
+				indexMid = index2;//循环终止条件是index2-index1 = 1
+				break;
+			}
+
+			indexMid = (index1 + index2) / 2;
+			//中间的元素，要不位于前面的递增序列(大于numbers[index1])
+			//要不位于后面的递增序列(小于numbers[index2])。
+			//注意特殊情况，如果numbers[index2] = numbers[index1] = numbers[indexMid]
+			//如{1，0，1，1，1}和{1，1，1，0，1}这种情况时无法判断最小值是在前面的递增子序列，还是后面的递增子序列
+			//此时可以采用顺序查找
+
+			if (numbers[index1] == numbers[index2] && numbers[index1] == numbers[indexMid])
+			{
+				return minInOrder(numbers, index1, index2);
+			}
+
+			if (numbers[indexMid] >= numbers[index1])
+			{
+				index1 = indexMid;
+			}
+			else if (numbers[indexMid] <= numbers[index2])
+			{
+				index2 = indexMid;
+			}
+		}
+
+		return numbers[indexMid];
+	}
+
+	int minInOrder(int[] numbers, int index1, int index2)
+	{
+		int result = numbers[index1];
+		for (int i = index1 + 1; i <= index2; ++i)
+		{
+			if (result > numbers[i])
+			{
+				result = numbers[i];
+			}
+		}
+		return result;
+	}
+
+	public static void main(String[] args) throws Exception
+	{
+		int[] numbers =
+		{ 1, 0, 1, 1, 1 };
+		MinNumberInRotatedArray minNumberInRotatedArray = new MinNumberInRotatedArray();
+		int min = minNumberInRotatedArray.min(numbers, numbers.length);
+		System.out.println(min);
+	}
+
+}

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

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+package problem07;
+
+import org.junit.Test;
+
+import junit.framework.Assert;
+
+public class QueueWithTwoStackTest
+{
+	@Test
+	public void test() throws Exception
+	{
+		QueueWithTwoStack queue = new QueueWithTwoStack();
+		queue.appendTail("1");
+		queue.appendTail("2");
+		queue.appendTail("3");
+		
+		Assert.assertEquals("1", queue.deletedHead());
+		Assert.assertEquals("2", queue.deletedHead());
+		Assert.assertEquals("3", queue.deletedHead());
+	}
+}

swordForOffer/src/test/java/problem07/QueueWithTwoStackTest.java

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