動機

就硬幹

Problem

Given an array target and an integer n. In each iteration, you will read a number from  list = {1,2,3..., n}.

Build the target array using the following operations:

  • Push: Read a new element from the beginning list, and push it in the array.
  • Pop: delete the last element of the array.
  • If the target array is already built, stop reading more elements.

Return the operations to build the target array. You are guaranteed that the answer is unique.

 

Example 1:

Input: target = [1,3], n = 3Output: ["Push","Push","Pop","Push"]Explanation: Read number 1 and automatically push in the array -> [1]Read number 2 and automatically push in the array then Pop it -> [1]Read number 3 and automatically push in the array -> [1,3]

Example 2:

Input: target = [1,2,3], n = 3Output: ["Push","Push","Push"]

Example 3:

Input: target = [1,2], n = 4Output: ["Push","Push"]Explanation: You only need to read the first 2 numbers and stop.

Example 4:

Input: target = [2,3,4], n = 4Output: ["Push","Pop","Push","Push","Push"]

 

Constraints:

  • 1 <= target.length <= 100
  • 1 <= target[i] <= n
  • 1 <= n <= 100
  • target is strictly increasing.

Sol

class Solution:
    def buildArray(self, target: List[int], n: int) -> List[str]:
        i = 0
        ret = []
        for x in range(1,n+1):
            if i == len(target):
                return ret
            else:
                ret += "Push",

            if target[i] != x:
                ret += "Pop",
            else:
                i += 1
        return ret