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]
Example 2:
Input: target = [1,2,3], n = 3
Output: ["Push","Push","Push"]
Example 3:
Input: target = [1,2], n = 4
Output: ["Push","Push"]
Explanation: You only need to read the first 2 numbers and stop.
Example 4:
Input: target = [2,3,4], n = 4
Output: ["Push","Pop","Push","Push","Push"]
Solution
这个题的思路是循环遍历从1到n+1(不含n+1）,如果发现当前值在target里，那么往结果集里append字符串”Push”。否则，同时append “Push” 和 “Pop”，注意退出条件，当target被遍历完后，说明已经结束了，后面就没必要继续遍历了。
class Solution:
def buildArray(self, target: List[int], n: int) -> List[str]:
tc =0
res = []
for i in range(1,n+1):
if tc== len(target):
break
if i ==target[tc]:
res.append("Push")
tc +=1
else:
res.append("Push")
res.append("Pop")
return res
