[LeetCode]#1441. Build an Array With Stack Operations

Environment: Python 3.7

Key technique: append

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.

You are guaranteed that the target array is strictly increasing, only containing numbers between 1 to n inclusive.

Return the operations to build the target array.

You are guaranteed that the answer is unique.

Example 1:

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

Analysis:

  1. Check 1 in target and answer is yes. Add “Push” in list.
  2. Check 2 in target and answer is No. Add “Push” and “Pop” in list.
  3. Check 3 in target and answer is yes. Add “Push” in list.
  4. Return [‘Push’, ‘Push’, ‘Pop’, ‘Push’]

Solution:

class Solution:
def buildArray(self, target, n):
ans = []
move = 0
for i in range(1, n+1):
ans.append("Push")
move += 1
if i not in target:
ans.append("Pop")
move -= 1
if move == len(target):
break
return ans

Submission:

Reference:

https://zdyxry.github.io/2020/05/16/2020-%E7%AC%AC20%E5%91%A8-LeetCode-%E8%AE%B0%E5%BD%95/#more

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