lab10

lab10/ArrayHeap.java

@@ -27,24 +27,21 @@ public ArrayHeap() {
      * Returns the index of the node to the left of the node at i.
      */
     private static int leftIndex(int i) {
-        /* TODO: Your code here! */
-        return 0;
+        return 2 * i;
     }
 
     /**
      * Returns the index of the node to the right of the node at i.
      */
     private static int rightIndex(int i) {
-        /* TODO: Your code here! */
-        return 0;
+        return 2 * i + 1;
     }
 
     /**
      * Returns the index of the node that is the parent of the node at i.
      */
     private static int parentIndex(int i) {
-        /* TODO: Your code here! */
-        return 0;
+        return i / 2;
     }
 
     /**
@@ -106,9 +103,15 @@ private int min(int index1, int index2) {
     private void swim(int index) {
         // Throws an exception if index is invalid. DON'T CHANGE THIS LINE.
         validateSinkSwimArg(index);
-
-        /** TODO: Your code here. */
-        return;
+        // 0. check if the given node's parent is index 0 or null;
+        if (parentIndex(index) == 0) return;
+        // 1. check if the given node is smaller than its parent
+        // 2. if not, return
+        // 3. if yes, get the parent index,
+        // and swap parent node and this node then swim from there
+        if (min(index, parentIndex(index)) != index) return;
+        swap(index, parentIndex(index));
+        swim(parentIndex(index));
     }
 
     /**
@@ -117,8 +120,13 @@ private void swim(int index) {
     private void sink(int index) {
         // Throws an exception if index is invalid. DON'T CHANGE THIS LINE.
         validateSinkSwimArg(index);
-
-        /** TODO: Your code here. */
+        // 1. if the current node < the min(children), swap it to that children
+        //      check both children
+        int minChildIndex = min(leftIndex(index), rightIndex(index));
+        if (minChildIndex > size) return;
+        if (min(index, minChildIndex) == index) return;
+        swap(index, minChildIndex);
+        sink(minChildIndex);
         return;
     }
 
@@ -133,7 +141,12 @@ public void insert(T item, double priority) {
             resize(contents.length * 2);
         }
 
-        /* TODO: Your code here! */
+        // 1. add the item to the end of contents
+        // 2. swim it
+        Node newNode = new Node(item, priority);
+        size += 1;
+        contents[size] = newNode;
+        swim(size);
     }
 
     /**
@@ -142,8 +155,11 @@ public void insert(T item, double priority) {
      */
     @Override
     public T peek() {
-        /* TODO: Your code here! */
-        return null;
+        // what is the smallest priority value index?
+        //      it must have the highest priority in the heap
+        // if correctly understood, the index should start from 1
+        //      because there's nothing at index 0;
+        return getNode(1).item();
     }
 
     /**
@@ -157,8 +173,12 @@ public T peek() {
      */
     @Override
     public T removeMin() {
-        /* TODO: Your code here! */
-        return null;
+        T returnNode = peek();
+        swap(size, 1);
+        contents[size] = null;
+        size -= 1;
+        sink(1);
+        return returnNode;
     }
 
     /**
@@ -180,8 +200,24 @@ public int size() {
      */
     @Override
     public void changePriority(T item, double priority) {
-        /* TODO: Your code here! */
-        return;
+        // 1. find the node, otherwise return nothing;
+        int targetIndex = 0;
+        for (int i = 1; i <= size; i++) {
+            if (contents[i].item().equals(item)) {
+                targetIndex = i;
+                break;
+            }
+        }
+        // 2. update its priority
+        Node updatedNode = new Node(item, priority);
+        contents[targetIndex] = updatedNode;
+        // 3. compare the updated node with its parent and minChild
+        //      to determine if it should swim (p) or sink(c)
+        int p = parentIndex(targetIndex);
+        int c = min(leftIndex(targetIndex), rightIndex(targetIndex));
+        if (min(targetIndex, p) == targetIndex) swim(p);
+        else if (min(targetIndex, c) == c) sink(c);
+        else return;
     }
 
     /**

lab10/lab10.iml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" name="javalib" level="project" />
+  </component>
+</module>

lab10/out/production/lab10/lab10.iml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" name="javalib" level="project" />
+  </component>
+</module>