439. Ternary Expression Parser
Given a string representing arbitrarily nested ternary expressions, calculate the result of the expression. You can always assume that the given expression is valid and only consists of digits 0-9
, ?
, :
, T
and F
(T
and F
represent True and False respectively).
Note:
- The length of the given string is ≤ 10000.
- Each number will contain only one digit.
- The conditional expressions group right-to-left (as usual in most languages).
- The condition will always be either
T
orF
. That is, the condition will never be a digit. - The result of the expression will always evaluate to either a digit
0-9
,T
orF
.
Example 1:
Input: "T?2:3" Output: "2" Explanation: If true, then result is 2; otherwise result is 3.
Example 2:
Input: "F?1:T?4:5" Output: "4" Explanation: The conditional expressions group right-to-left. Using parenthesis, it is read/evaluated as: "(F ? 1 : (T ? 4 : 5))" "(F ? 1 : (T ? 4 : 5))" -> "(F ? 1 : 4)" or -> "(T ? 4 : 5)" -> "4" -> "4"
Example 3:
Input: "T?T?F:5:3" Output: "F" Explanation: The conditional expressions group right-to-left. Using parenthesis, it is read/evaluated as: "(T ? (T ? F : 5) : 3)" "(T ? (T ? F : 5) : 3)" -> "(T ? F : 3)" or -> "(T ? F : 5)" -> "F" -> "F"
Rust Solution
struct Solution;
impl Solution {
fn parse_ternary(expression: String) -> String {
let expression: Vec<char> = expression.chars().collect();
Self::parse(&expression).iter().copied().collect()
}
fn parse(expression: &[char]) -> &[char] {
let n = expression.len();
if n == 1 {
expression
} else {
let mut count = 1;
for i in 2..n {
if expression[i] == '?' {
count += 1;
continue;
}
if expression[i] == ':' {
count -= 1;
if count == 0 {
return if expression[0] == 'T' {
Self::parse(&expression[2..i])
} else {
Self::parse(&expression[i + 1..])
};
}
}
}
&[]
}
}
}
#[test]
fn test() {
let expression = "T?2:3".to_string();
let res = "2".to_string();
assert_eq!(Solution::parse_ternary(expression), res);
let expression = "F?1:T?4:5".to_string();
let res = "4".to_string();
assert_eq!(Solution::parse_ternary(expression), res);
let expression = "T?T?F:5:3".to_string();
let res = "F".to_string();
assert_eq!(Solution::parse_ternary(expression), res);
}
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