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0735-asteroid-collision/0735-asteroid-collision.py

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+class Solution:
+    def asteroidCollision(self, asteroids: List[int]) -> List[int]:
+        """
+        Complexities:
+        Time:  O(n)
+        Space: O(n)
+
+        where n = len(asteroids)
+        """
+
+        # iterate left to right
+        # - if right (+ve), keep stack
+        # - if left (-ve), compare/consume top of stack
+        # - - if left consume all of stack, add to output (it will survive)
+
+        stack = []
+        survivedAsteroids = []
+        for i in range(len(asteroids)):
+            if asteroids[i] > 0:
+                stack.append(asteroids[i])
+            else:
+                isDestroyed = False
+                while len(stack) > 0 and abs(asteroids[i]) >= stack[-1]:
+                    if abs(asteroids[i]) == stack[-1]:
+                        isDestroyed = True
+                        stack.pop()
+                        break
+                    stack.pop()
+                
+                if len(stack) == 0 and not isDestroyed:
+                    survivedAsteroids.append(asteroids[i])
+
+
+        # also return stack
+        survivedAsteroids += stack
+
+        return survivedAsteroids