Implement week 2 assignment 3

src/heap.rs

@@ -1,54 +1,127 @@
 #[derive(Debug)]
 struct MinHeap<T> {
     nodes: Vec<T>,
-    size: usize,
 }
 
-fn parent_index(i: usize) -> usize {
-	(i + 1) / 2 - 1
+fn parent_index(index: usize) -> usize {
+	(index + 1) / 2 - 1
 }
 
-fn child_index(i: usize) -> (usize, usize) {
-	((i + 1) * 2 - 1, (i + 1) * 2 + 1 - 1)
+fn child_indices(index: usize) -> (usize, usize) {
+	((index + 1) * 2 - 1, (index + 1) * 2 + 1 - 1)
 }
 
 impl<T: std::cmp::PartialOrd> MinHeap<T> {
     fn new() -> Self {
-        Self {
-            nodes: Vec::with_capacity(128),
-            size: 0,
-        }
+        Self { nodes: Vec::with_capacity(128) }
+    }
+
+    fn smaller_than_parent(&self, index: usize) -> bool {
+    	if index == 0 {
+    		false
+    	} else {
+
+			self.nodes[index] < self.nodes[parent_index(index)]
+    	}
+    }
+
+    fn bubble_up(&mut self, index: usize) -> usize {
+    	let parent_index = parent_index(index);
+    	self.nodes.swap(index, parent_index);
+    	parent_index
     }
 
     fn insert(&mut self, e: T) -> () {
-        // append at the end
         self.nodes.push(e);
-        self.size += 1;
-        let last_index = self.size - 1;
-        let mut swap_index = self.size - 1;
+        let last = self.nodes.len() - 1;
+        let mut bubble_index = last;
 
-        while swap_index != 0 && self.nodes[last_index] < self.nodes[parent_index(swap_index)] {
-            swap_index = parent_index(swap_index);
+        while self.smaller_than_parent(bubble_index) {
+        	bubble_index = self.bubble_up(bubble_index);
         }
-        self.nodes.swap(last_index, swap_index);
+    }
+
+    fn greater_than_children(&self, index: usize) -> bool {
+    	let length = self.nodes.len();
+    	let (left_index, right_index) = child_indices(index);
+    	if left_index < length && self.nodes[index] > self.nodes[left_index]  {
+    		true
+    	} else if right_index < length && self.nodes[index] > self.nodes[right_index] {
+    		true
+    	} else {
+	    	false
+    	}
+    }
+
+    fn bubble_down(&mut self, index: usize) -> usize {
+    	let length = self.nodes.len();
+    	let (left_index, right_index) = child_indices(index);
+    	let mut target_index = index;
+
+    	if left_index < length && self.nodes[target_index] > self.nodes[left_index] {
+    		target_index = left_index;
+    	}
+
+    	if right_index < length && self.nodes[right_index] < self.nodes[target_index] {
+    		target_index = right_index;
+    	}
+    	self.nodes.swap(index, target_index);
+    	target_index
     }
 
     fn extract_min(&mut self) -> T {
-    	if self.size == 0 {
+    	if self.nodes.len() == 0 {
     		panic!("Cannot extract key from empty heap");
     	}
-    	self.nodes.swap(0, self.size - 1);
-    	let child_indices = child_index(0);
-    	println!("{:?}", child_indices);
-    	self.nodes.pop().unwrap()
+
+    	let mut bubble_index = 0;
+    	let last = self.nodes.len() - 1;
+    	self.nodes.swap(bubble_index, last);
+    	let result = self.nodes.pop().unwrap();
+
+    	while self.greater_than_children(bubble_index) {
+    		bubble_index = self.bubble_down(bubble_index);
+    	}
+
+    	result
+    }
+
+    fn size(&self) -> usize {
+    	self.nodes.len()
     }
 }
 
-pub fn heap(v: &Vec<u32>) -> () {
-    let mut mh: MinHeap<u32> = MinHeap::new();
-    for i in 0..5 {
-        mh.insert(v[i]);
-        println!("{:?}", mh);
+pub fn heap(v: &Vec<i32>) -> i32 {
+    let mut hl: MinHeap<i32> = MinHeap::new();
+    let mut hh: MinHeap<i32> = MinHeap::new();
+
+	let mut iter = v.into_iter();
+    let mut current_median = *iter.next().unwrap();
+    let mut median_sum = current_median;
+    hl.insert(-current_median);
+
+    for e in iter {
+    	let e = *e;
+    	if e < current_median {
+    		hl.insert(-e);
+    	} else {
+    		hh.insert(e);
+    	}
+
+    	while hl.size() < hh.size() {
+    		let e = hh.extract_min();
+    		hl.insert(-e);
+    	}
+
+    	while hl.size() > hh.size() + 1 {
+    		let e = -hl.extract_min();
+    		hh.insert(e);
+    	}
+
+    	current_median = -hl.extract_min();
+    	median_sum = (median_sum + current_median) % 10000;
+    	hl.insert(-current_median);
     }
-    mh.extract_min();
+
+    median_sum
 }

src/main.rs

@@ -42,8 +42,8 @@ fn c1a4() {
             smallest_min_cut = new_min_cut;
         }
     }
-    // 17
     println!("c1a4={:?}", smallest_min_cut);
+    // 17
 }
 
 #[allow(dead_code)]
@@ -71,7 +71,8 @@ fn c2a2() {
 #[allow(dead_code)]
 fn c2a3() {
     let vec = util::read_to_vector("data/c2a3.txt").unwrap();
-    heap(&vec);
+    let r = heap(&vec);
+    println!("c2a3={:?}", r);
 }
 
 fn main() {

src/util.rs

@@ -23,7 +23,7 @@ pub struct DirectedWeightedGraph {
     pub distance: Vec<usize>,
 }
 
-pub fn read_to_vector(path: &str) -> Result<Vec<u32>, io::Error> {
+pub fn read_to_vector(path: &str) -> Result<Vec<i32>, io::Error> {
     let file = File::open(path)?;
     let br = BufReader::new(file);
     let mut v = Vec::new();