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"]
Constraints:
1 <= target.length <= 100
1 <= target[i] <= 100
1 <= n <= 100
target
is strictly increasing.
A:
class Solution { public: vector<string> buildArray(vector<int>& target, int n) { vector<string> res; int index = 0; for(int i =1;i<=n; ++i){ if(index< target.size()){ //otherwise stop reading early res.push_back("Push"); if(i < target[index] ){ res.push_back("Pop"); } if(target[index] == i){ index ++; } } } return res; } };
这个题目,错在, 一开始没有读完所有的例子。
导致,没有意识到early stop 的问题。 Example 3
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