feat: add leetcode75 day31

add leetcode75 day31

Author: hj.tian

leetcode75/day31_155.py

@@ -0,0 +1,46 @@
+from typing import List, Tuple
+
+
+class MinStack:
+    """
+    stack
+    (-3, -3)
+    (0, -2)
+    (-2, -2)
+    """
+
+    def __init__(self):
+        self.stack: List[Tuple[int, int]] = []
+
+    def push(self, val: int) -> None:
+        if len(self.stack) == 0:
+            self.stack.append((val, val))
+        else:
+            cur_mins = self.stack[-1][1]
+            if val < cur_mins:
+                self.stack.append((val, val))
+            else:
+                self.stack.append((val, cur_mins))
+
+    def pop(self) -> None:
+        self.stack = self.stack[:-1]
+
+    def top(self) -> int:
+        if self.stack:
+            return self.stack[-1][0]
+
+    def getMin(self) -> int:
+        if self.stack:
+            return self.stack[-1][1]
+
+
+if __name__ == "__main__":
+    # Your MinStack object will be instantiated and called as such:
+    obj = MinStack()
+    obj.push(-2)
+    obj.push(0)
+    obj.push(-3)
+    assert obj.getMin() == -3
+    obj.pop()
+    assert obj.top() == 0
+    assert obj.getMin() == -2

leetcode75/day31_208.py

@@ -0,0 +1,59 @@
+class Trie:
+    """
+    root {}
+
+    a {a: {}}
+
+    p {a: {p: {}}}
+
+    p {a: {p: {p: {}}}}
+
+    l {a: {p: {p: {l: {}}}}}
+
+    e {a: {p: {p: {l: {e: {}}}}}}
+
+    $ {a: {p: {p: {l: {e: {$:$}}}}}}
+
+    after insert app
+    {a: {p: {p: {
+                    l: {e: {$:$}},
+                    $: $
+    }}}}
+    """
+
+    def __init__(self):
+        self.root = {}
+
+    def insert(self, word: str) -> None:
+        root = self.root
+        for char in word:
+            if char not in root:
+                root[char] = {}
+            root = root[char]
+        root["$"] = "$"
+
+    def search(self, word: str) -> bool:
+        root = self.root
+        for char in word:
+            if char not in root:
+                return False
+            root = root[char]
+        return root.get("$") == "$"
+
+    def startsWith(self, prefix: str) -> bool:
+        root = self.root
+        for char in prefix:
+            if char not in root:
+                return False
+            root = root[char]
+        return True
+
+
+if __name__ == "__main__":
+    trie = Trie()
+    trie.insert("apple")
+    assert trie.search("apple") is True
+    assert trie.search("app") is False
+    assert trie.startsWith("app") is True
+    trie.insert("app")
+    assert trie.search("app") is True

leetcode75/day31_232.py

@@ -0,0 +1,56 @@
+class MyQueue:
+    """
+    stack: 后入先出
+    queue: 先入先出
+
+    stack1      stack2
+
+    |   |       |   |
+    | 2 |       |   |
+    | 1 |       |   |
+
+    push 操作: 往 stack1 里压
+    peek 操作:
+        1. stack2    空: stack1 所有出栈并依次压入 stack2, 返回 stack2 栈顶
+        2. stack2  非空: 直接返回 stack2 栈顶
+    pop 操作:
+        1. stack2    空: stack1 所有出栈并依次压入 stack2, 弹出 stack2 栈顶
+        2. stack2  非空: 直接弹出 stack2 栈顶
+    empty:
+        stack2 is empty and stack1 is empty
+    """
+
+    def __init__(self):
+        self.stack1 = []
+        self.stack2 = []
+
+    def push(self, x: int) -> None:
+        self.stack1.append(x)
+
+    def pop(self) -> int:
+        ans = self.peek()
+        self.stack2 = self.stack2[:-1]
+        return ans
+
+    def peek(self) -> int:
+        if len(self.stack2) == 0:
+            self.stack2 = self.stack1[::-1]
+            self.stack1 = []
+        if len(self.stack2) > 0:
+            return self.stack2[-1]
+
+    def empty(self) -> bool:
+        return len(self.stack1) == len(self.stack2) == 0
+
+
+if __name__ == "__main__":
+    # Your MyQueue object will be instantiated and called as such:
+    obj = MyQueue()
+    obj.push(1)
+    obj.push(2)
+    assert obj.peek() == 1
+    assert obj.pop() == 1
+    assert obj.empty() is False
+    assert obj.pop() == 2
+    assert obj.pop() is None
+    assert obj.empty() is True