heap

SoniaComp · SoniaComp · commit b51fb0ff574f · 2021-03-21T22:46:12.000+09:00
diff --git a/study/graph/graph_bfs.queue.py b/study/graph/graph_bfs.queue.py
@@ -1,3 +1,4 @@
+graph = []
 def iterative_dfs(start_v):
   discovered = [start_v]
   queue = [start_v]
diff --git a/study/graph/graph_dfs_recursive.py b/study/graph/graph_dfs_recursive.py
@@ -1,3 +1,4 @@
+graph = []
 def recursive_dfs(v, discovered=[]):
   discovered.append(v)
   for w in graph[v]:
diff --git a/study/graph/graph_dfs_stack.py b/study/graph/graph_dfs_stack.py
@@ -1,3 +1,4 @@
+graph = []
 def iterative_dfs(start_v):
   discovored = []
   stack = [start_v]
diff --git a/study/heap/BinaryHeap.py b/study/heap/BinaryHeap.py
@@ -0,0 +1,42 @@
+class BinaryHeap(object):
+  def __init__(self):
+    self.items = [None]
+  
+  def __len__(self):
+    return len(self.items) - 1
+
+  def _percolate_up(self):
+    i = len(self)
+    parent = i // 2
+    while parent >= 0:
+      if self.items[i] < self.items[parent]:
+        self.items[parent], self.items[i] = \
+          self.items[i], self.items[parent]
+        i = parent
+        parent = i//2
+    
+  def insert(self, k):
+    self.items.append(k)
+    self._percolate_up()
+
+  def _percolalte_down(self, idx):
+    left = idx * 2
+    right = idx * 2 + 1
+    smallest = idx
+
+    if left <= len(self) and self.items[left] < self.items[smallest]:
+      smallest = left
+
+    if right <= len(self) and self.items[right] < self.items[smallest]:
+      smallest = right
+    
+    if smallest != idx:
+      self.items[idx], self.items[smallest] = self.items[smallest], self.items[idx]
+      self._percolalte_down(smallest)
+
+  def extract(self):
+    extracted = self.items[1]
+    self.items[1] = self.items[len(self)]
+    self.items.pop()
+    self._percolalte_down(1)
+    return extracted
diff --git a/study/heap/leet215.py b/study/heap/leet215.py
@@ -0,0 +1,23 @@
+import heapq
+
+class Solution:
+    def findKthLargest(self, nums: List[int], k: int) -> int:
+        heapq.heapify(nums)
+        # heap = list()
+        # for n in nums:
+        #     heapq.heappush(heap, -n)
+          # heapq 모듈은 최소 힙만 지원하므로 음수로 저장한 다음 가장 낮은 수부터 추출
+
+        # for _ in range(k):
+            # heapq.heappop(heap)
+        for _ in range(len(nums)-k):
+            heapq.heappop(nums)
+        
+        # return -heapq.heappop(heap)
+        return heapq.heappop(nums)
+
+        # nlargest 이용
+        # return heapq.nlargest(k, nums)[-1]
+
+        # 정렬
+        # return sorted(nums, reverse=True)[k-1]

Original file line number	Diff line number	Diff line change
`@@ -1,3 +1,4 @@`
	`1`	`+graph = []`
`1`	`2`	`def iterative_dfs(start_v):`
`2`	`3`	`discovered = [start_v]`
`3`	`4`	`queue = [start_v]`
Original file line number	Diff line number	Diff line change
`@@ -1,3 +1,4 @@`
	`1`	`+graph = []`
`1`	`2`	`def recursive_dfs(v, discovered=[]):`
`2`	`3`	`discovered.append(v)`
`3`	`4`	`for w in graph[v]:`