LeetCode in Kotlin
224. Basic Calculator
Hard
Given a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation.
Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as eval().
Example 1:
Input: s = “1 + 1”
Output: 2
Example 2:
Input: s = “ 2-1 + 2 “
Output: 3
Example 3:
Input: s = “(1+(4+5+2)-3)+(6+8)”
Output: 23
Constraints:
1 <= s.length <= 3 * 105sconsists of digits,'+','-','(',')', and' '.srepresents a valid expression.'+'is not used as a unary operation (i.e.,"+1"and"+(2 + 3)"is invalid).'-'could be used as a unary operation (i.e.,"-1"and"-(2 + 3)"is valid).- There will be no two consecutive operators in the input.
- Every number and running calculation will fit in a signed 32-bit integer.
Solution
class Solution {
private var i = 0
fun calculate(s: String): Int {
val ca = s.toCharArray()
return helper(ca)
}
private fun helper(ca: CharArray): Int {
var num = 0
var prenum = 0
var isPlus = true
while (i < ca.size) {
val c = ca[i]
if (c != ' ') {
if (c >= '0' && c <= '9') {
num = if (num == 0) {
c.code - '0'.code
} else {
num * 10 + c.code - '0'.code
}
} else if (c == '+') {
prenum += num * if (isPlus) 1 else -1
isPlus = true
num = 0
} else if (c == '-') {
prenum += num * if (isPlus) 1 else -1
num = 0
isPlus = false
} else if (c == '(') {
i++
prenum += helper(ca) * if (isPlus) 1 else -1
isPlus = true
num = 0
} else if (c == ')') {
return prenum + num * if (isPlus) 1 else -1
}
}
i++
}
return prenum + num * if (isPlus) 1 else -1
}
}