parentheses_check.rs

/// This is a direct line-by-line translation from C++ solution:
/// https://github.com/LyashenkoGS/cpluplus_study/blob/master/test/Solution.cpp
///
/// The point is to show that Rust can save your ass.

struct Solution {}

impl Solution {
    fn processParenthesis(stack1: &mut Vec<char>, item: char, openSign: char, closingSign: char) {
        if item == openSign {
            stack1.push(item);
        } else if item == closingSign {
            let top = stack1.last();
            if top == openSign {  // Rust produces a compilation error here:
//                    ^^^^^^^^ expected enum `std::option::Option`, found char
//          = note: expected type `std::option::Option<&char>`
//                  found type `char`
//
//          This means that `stack1.last()` returns either the last value or None,
//          and we MUST handle this case in our code. Here is a naive approach, we
//          assume that None will never occur and we just force Rust to get the
//          last value:
//          if *top.unwrap() == openSign {
//
//          Rust will agree to compile this code, but it may now get into the runtime error:
//                  10: qq4::Solution::processParenthesis
//                             at src/main.rs:14
//                  11: qq4::Solution::isValid
//                             at src/main.rs:43
//                  12: qq4::mytest
//                             at src/main.rs:56
//
//          I hope you can get the root cause of the error.
                stack1.pop();
            }
        }
    }

    fn isValid(s: &str) -> bool {
        let mut stack = Vec::new();
        for item in s.chars() {
            Self::processParenthesis(&mut stack,item,'(',')');
            Self::processParenthesis(&mut stack,item,'[',']');
            Self::processParenthesis(&mut stack,item,'{','}');
        }
        return stack.is_empty();
    }
}

#[test]
fn mytest() {
    assert!(Solution::isValid("[]"));
    assert!(Solution::isValid("[]()"));
    assert!(Solution::isValid("[]{}()"));
    assert!(Solution::isValid("))"));
}