update

Author: wuduhren

problems/python3/car-fleet.py

@@ -0,0 +1,16 @@
+class Solution:
+    def carFleet(self, target: int, position: List[int], speed: List[int]) -> int:
+        N = len(position)
+        
+        timeInfo = []
+        for i in range(N):
+            timeInfo.append((position[i], (target-position[i])/speed[i]))
+        timeInfo.sort(reverse=True)
+        
+        stack = []
+        for _, time in timeInfo:
+            stack.append(time)
+            if len(stack)>=2 and stack[-2]>=stack[-1]:
+                stack.pop()
+        
+        return len(stack)

problems/python3/daily-temperatures.py

@@ -0,0 +1,12 @@
+class Solution:
+    def dailyTemperatures(self, temperatures: List[int]) -> List[int]:
+        ans = [0]*len(temperatures)
+        stack = []
+        
+        for i, temp in enumerate(temperatures):
+            while stack and stack[-1][0]<temp:
+                prevTemp, prevIndex = stack.pop()
+                ans[prevIndex] = i-prevIndex
+            stack.append((temp, i))
+        
+        return ans

problems/python3/evaluate-reverse-polish-notation.py

@@ -0,0 +1,22 @@
+class Solution:
+    def evalRPN(self, tokens: List[str]) -> int:
+        operators = set(['+', '-', '*', '/'])
+        stack = []
+        
+        for c in tokens:
+            if c in operators:
+                n2 = stack.pop()
+                n1 = stack.pop()
+                
+                if c=='+':
+                    stack.append(n1+n2)
+                elif c=='-':
+                    stack.append(n1-n2)
+                elif c=='*':
+                    stack.append(n1*n2)
+                elif c=='/':
+                    stack.append(int(n1/n2))
+            else:
+                stack.append(int(c))
+        
+        return stack.pop()

problems/python3/generate-parentheses.py

@@ -0,0 +1,20 @@
+class Solution:
+    def generateParenthesis(self, n: int) -> List[str]:
+        def helper(parentheses, left, right):
+            if len(parentheses)==n*2:
+                ans.append("".join(parentheses))
+                return
+            
+            if left<n:
+                parentheses.append('(')
+                helper(parentheses, left+1, right)
+                parentheses.pop()
+            
+            if left>right:
+                parentheses.append(')')
+                helper(parentheses, left, right+1)
+                parentheses.pop()
+        
+        ans = []
+        helper([], 0, 0)
+        return ans

problems/python3/min-stack.py

@@ -0,0 +1,23 @@
+#"stack" is just a normal stack.
+#"minStack" stores the min of the stack element in the same position.
+#i.e. At the time stack[x] put in to the stack. minStack[x] is the min.
+
+class MinStack:
+
+    def __init__(self):
+        self.stack = []
+        self.minStack = []
+
+    def push(self, val: int) -> None:
+        self.stack.append(val)
+        self.minStack.append(val if (not self.minStack or val<self.minStack[-1]) else self.minStack[-1])
+
+    def pop(self) -> None:
+        self.minStack.pop()
+        return self.stack.pop()
+        
+    def top(self) -> int:
+        return self.stack[-1]
+        
+    def getMin(self) -> int:
+        return self.minStack[-1]