- Difficulty: Hard
- Tags: LeetCode, Hard, Array, Math, Backtracking, leetcode-679, O(1), DFS
Problem
You are given an integer array cards
of length 4
. You have four cards, each containing a number in the range [1, 9]
. You should arrange the numbers on these cards in a mathematical expression using the operators ['+', '-', '*', '/']
and the parentheses '('
and ')'
to get the value 24.
You are restricted with the following rules:
- The division operator
'/'
represents real division, not integer division.- For example,
4 / (1 - 2 / 3) = 4 / (1 / 3) = 12
.
- For example,
- Every operation done is between two numbers. In particular, we cannot use
'-'
as a unary operator.- For example, if
cards = [1, 1, 1, 1]
, the expression"-1 - 1 - 1 - 1"
is not allowed.
- For example, if
- You cannot concatenate numbers together
- For example, if
cards = [1, 2, 1, 2]
, the expression"12 + 12"
is not valid.
- For example, if
Return true
if you can get such expression that evaluates to 24
, and false
otherwise.
Example 1:
Input: cards = [4,1,8,7] Output: true Explanation: (8-4) * (7-1) = 24
Example 2:
Input: cards = [1,2,1,2] Output: false
Constraints:
cards.length == 4
1 <= cards[i] <= 9