diff --git a/.metadata/.plugins/org.eclipse.core.resources/.history/57/507debe8dfa80017102fc75ae426c58e b/.metadata/.plugins/org.eclipse.core.resources/.history/57/507debe8dfa80017102fc75ae426c58e
new file mode 100644
index 0000000..f42de36
--- /dev/null
+++ b/.metadata/.plugins/org.eclipse.core.resources/.history/57/507debe8dfa80017102fc75ae426c58e
@@ -0,0 +1,7 @@
+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.7
+org.eclipse.jdt.core.compiler.compliance=1.7
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.source=1.7
diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_10_of_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_10_of_Algorithm/.markers.snap
index 39a1322..766ddb4 100644
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index 39a1322..766ddb4 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_11_of_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_11_of_Algorithm/.markers.snap
index 39a1322..766ddb4 100644
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index 39a1322..766ddb4 100644
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index 39a1322..766ddb4 100644
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index 39a1322..766ddb4 100644
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index 39a1322..766ddb4 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_16_of_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_16_of_Algorithm/.markers.snap
index 39a1322..766ddb4 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_22_of_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_22_of_Algorithm/.markers.snap
index 7487dcb..0eec99a 100644
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index 8e9cfc7..f6dc3a4 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_23_of_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_23_of_Algorithm/.markers.snap
index ef1cd04..fd2284e 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_24_of_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_24_of_Algorithm/.markers.snap
index 879fbb7..96488ad 100644
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index 0b992ea..464a957 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_25_of_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_25_of_Algorithm/.markers.snap
index d835df1..3873ade 100644
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index d835df1..3873ade 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_26_0f_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_26_0f_Algorithm/.markers.snap
index 150a164..b18e8e2 100644
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index 3cf252b..d835df1 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_27_of_Algorithm/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.projects/Chapter_27_of_Algorithm/.markers.snap
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index 0000000..91d6c54
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.root/.markers.snap b/.metadata/.plugins/org.eclipse.core.resources/.root/.markers.snap
index ea623e6..795cf87 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.safetable/org.eclipse.core.resources b/.metadata/.plugins/org.eclipse.core.resources/.safetable/org.eclipse.core.resources
index 0737672..587fa3f 100644
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diff --git a/.metadata/.plugins/org.eclipse.core.resources/.snap b/.metadata/.plugins/org.eclipse.core.resources/.snap
index ab2aa04..908d3d6 100644
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diff --git a/.metadata/.plugins/org.eclipse.jdt.core/3198679199.index b/.metadata/.plugins/org.eclipse.jdt.core/3198679199.index
new file mode 100644
index 0000000..5fe1ed0
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diff --git a/.metadata/.plugins/org.eclipse.jdt.core/savedIndexNames.txt b/.metadata/.plugins/org.eclipse.jdt.core/savedIndexNames.txt
index 135e5fc..614bab1 100644
--- a/.metadata/.plugins/org.eclipse.jdt.core/savedIndexNames.txt
+++ b/.metadata/.plugins/org.eclipse.jdt.core/savedIndexNames.txt
@@ -1,6 +1,7 @@
 INDEX VERSION 1.126+/home/liyafei/test/IntroductionToAlgorithm/.metadata/.plugins/org.eclipse.jdt.core
 852849552.index
 973379314.index
+3198679199.index
 3390519334.index
 3267812676.index
 2802546564.index
diff --git a/.metadata/.plugins/org.eclipse.jdt.core/variablesAndContainers.dat b/.metadata/.plugins/org.eclipse.jdt.core/variablesAndContainers.dat
index 972df0d..997702b 100644
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diff --git a/Chapter_27_of_Algorithm/.classpath b/Chapter_27_of_Algorithm/.classpath
new file mode 100644
index 0000000..fb565a5
--- /dev/null
+++ b/Chapter_27_of_Algorithm/.classpath
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.7"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>
diff --git a/Chapter_27_of_Algorithm/.project b/Chapter_27_of_Algorithm/.project
new file mode 100644
index 0000000..16958b4
--- /dev/null
+++ b/Chapter_27_of_Algorithm/.project
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>Chapter_27_of_Algorithm</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>
diff --git a/Chapter_27_of_Algorithm/.settings/org.eclipse.jdt.core.prefs b/Chapter_27_of_Algorithm/.settings/org.eclipse.jdt.core.prefs
new file mode 100644
index 0000000..7341ab1
--- /dev/null
+++ b/Chapter_27_of_Algorithm/.settings/org.eclipse.jdt.core.prefs
@@ -0,0 +1,11 @@
+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.7
+org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
+org.eclipse.jdt.core.compiler.compliance=1.7
+org.eclipse.jdt.core.compiler.debug.lineNumber=generate
+org.eclipse.jdt.core.compiler.debug.localVariable=generate
+org.eclipse.jdt.core.compiler.debug.sourceFile=generate
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.source=1.7