24 Game
hard · verified · 59.4% accepted · 1,888 likes · top 57%
array · math · backtracking
Description
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.
- 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.
- You cannot concatenate numbers together
- For example, if cards = [1, 2, 1, 2], the expression "12 + 12" is not valid.
Return true if you can get such expression that evaluates to 24, and false otherwise.
Example 1:
Example 2:
Solution