Improve infix to postfix notation algorithm

Cargo.toml

@@ -145,6 +145,7 @@ unwrap_in_result = { level = "allow", priority = 1 }
 unwrap_used = { level = "allow", priority = 1 }
 use_debug = { level = "allow", priority = 1 }
 wildcard_enum_match_arm = { level = "allow", priority = 1 }
+renamed_function_params = { level = "allow", priority = 1 }
 # nursery-lints:
 branches_sharing_code = { level = "allow", priority = 1 }
 cognitive_complexity = { level = "allow", priority = 1 }
@@ -160,5 +161,9 @@ redundant_clone = { level = "allow", priority = 1 }
 suboptimal_flops = { level = "allow", priority = 1 }
 suspicious_operation_groupings = { level = "allow", priority = 1 }
 use_self = { level = "allow", priority = 1 }
+while_float = { level = "allow", priority = 1 }
+needless_pass_by_ref_mut = { level = "allow", priority = 1 }
 # cargo-lints:
 cargo_common_metadata = { level = "allow", priority = 1 }
+# style-lints:
+doc_lazy_continuation = { level = "allow", priority = 1 }

DIRECTORY.md

@@ -63,7 +63,6 @@
     * [Graph](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/graph.rs)
     * [Hash Table](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/hash_table.rs)
     * [Heap](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/heap.rs)
-    * [Infix To Postfix](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/infix_to_postfix.rs)
     * [Lazy Segment Tree](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/lazy_segment_tree.rs)
     * [Linked List](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/linked_list.rs)
     * [Postfix Evaluation](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/postfix_evaluation.rs)
@@ -206,6 +205,7 @@
     * [Interest](https://github.com/TheAlgorithms/Rust/blob/master/src/math/interest.rs)
     * [Interpolation](https://github.com/TheAlgorithms/Rust/blob/master/src/math/interpolation.rs)
     * [Interquartile Range](https://github.com/TheAlgorithms/Rust/blob/master/src/math/interquartile_range.rs)
+    * [Infix To Postfix](https://github.com/TheAlgorithms/Rust/blob/master/src/math/infix_to_postfix.rs)
     * [Karatsuba Multiplication](https://github.com/TheAlgorithms/Rust/blob/master/src/math/karatsuba_multiplication.rs)
     * [Lcm Of N Numbers](https://github.com/TheAlgorithms/Rust/blob/master/src/math/lcm_of_n_numbers.rs)
     * [Leaky Relu](https://github.com/TheAlgorithms/Rust/blob/master/src/math/leaky_relu.rs)

src/data_structures/mod.rs

@@ -6,7 +6,6 @@ mod floyds_algorithm;
 pub mod graph;
 mod hash_table;
 mod heap;
-mod infix_to_postfix;
 mod lazy_segment_tree;
 mod linked_list;
 mod postfix_evaluation;
@@ -31,7 +30,6 @@ pub use self::graph::DirectedGraph;
 pub use self::graph::UndirectedGraph;
 pub use self::hash_table::HashTable;
 pub use self::heap::Heap;
-pub use self::infix_to_postfix::infix_to_postfix;
 pub use self::lazy_segment_tree::LazySegmentTree;
 pub use self::linked_list::LinkedList;
 pub use self::postfix_evaluation::evaluate_postfix;

src/math/infix_to_postfix.rs

@@ -0,0 +1,94 @@
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum InfixToPostfixError {
+    UnknownCharacter(char),
+    UnmatchedParent,
+}
+
+/// Function to convert [infix expression](https://en.wikipedia.org/wiki/Infix_notation) to [postfix expression](https://en.wikipedia.org/wiki/Reverse_Polish_notation)
+pub fn infix_to_postfix(infix: &str) -> Result<String, InfixToPostfixError> {
+    let mut postfix = String::new();
+    let mut stack: Vec<char> = Vec::new();
+
+    // Define the precedence of operators
+    let precedence = |op: char| -> u8 {
+        match op {
+            '+' | '-' => 1,
+            '*' | '/' => 2,
+            '^' => 3,
+            _ => 0,
+        }
+    };
+
+    for token in infix.chars() {
+        match token {
+            c if c.is_alphanumeric() => {
+                postfix.push(c);
+            }
+            '(' => {
+                stack.push('(');
+            }
+            ')' => {
+                while let Some(top) = stack.pop() {
+                    if top == '(' {
+                        break;
+                    }
+                    postfix.push(top);
+                }
+            }
+            '+' | '-' | '*' | '/' | '^' => {
+                while let Some(top) = stack.last() {
+                    if *top == '(' || precedence(*top) < precedence(token) {
+                        break;
+                    }
+                    postfix.push(stack.pop().unwrap());
+                }
+                stack.push(token);
+            }
+            other => return Err(InfixToPostfixError::UnknownCharacter(other)),
+        }
+    }
+
+    while let Some(top) = stack.pop() {
+        if top == '(' {
+            return Err(InfixToPostfixError::UnmatchedParent);
+        }
+
+        postfix.push(top);
+    }
+
+    Ok(postfix)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    macro_rules! test_infix_to_postfix {
+        ($($name:ident: $inputs:expr,)*) => {
+            $(
+                #[test]
+                fn $name() {
+                    let (infix, expected) = $inputs;
+                    assert_eq!(infix_to_postfix(infix), expected)
+                }
+            )*
+        }
+    }
+
+    test_infix_to_postfix! {
+        single_symbol: ("x", Ok(String::from("x"))),
+        simple_sum: ("x+y", Ok(String::from("xy+"))),
+        multiply_sum_left: ("x*(y+z)", Ok(String::from("xyz+*"))),
+        multiply_sum_right: ("(x+y)*z", Ok(String::from("xy+z*"))),
+        multiply_two_sums: ("(a+b)*(c+d)", Ok(String::from("ab+cd+*"))),
+        product_and_power: ("a*b^c", Ok(String::from("abc^*"))),
+        power_and_product: ("a^b*c", Ok(String::from("ab^c*"))),
+        product_of_powers: ("(a*b)^c", Ok(String::from("ab*c^"))),
+        product_in_exponent: ("a^(b*c)", Ok(String::from("abc*^"))),
+        regular_0: ("a-b+c-d*e", Ok(String::from("ab-c+de*-"))),
+        regular_1: ("a*(b+c)+d/(e+f)", Ok(String::from("abc+*def+/+"))),
+        regular_2: ("(a-b+c)*(d+e*f)", Ok(String::from("ab-c+def*+*"))),
+        unknown_character: ("(a-b)*#", Err(InfixToPostfixError::UnknownCharacter('#'))),
+        unmatched_paren: ("((a-b)", Err(InfixToPostfixError::UnmatchedParent)),
+    }
+}

src/math/mod.rs

@@ -34,6 +34,7 @@ mod gcd_of_n_numbers;
 mod geometric_series;
 mod greatest_common_divisor;
 mod huber_loss;
+mod infix_to_postfix;
 mod interest;
 mod interpolation;
 mod interquartile_range;
@@ -122,6 +123,7 @@ pub use self::greatest_common_divisor::{
     greatest_common_divisor_stein,
 };
 pub use self::huber_loss::huber_loss;
+pub use self::infix_to_postfix::infix_to_postfix;
 pub use self::interest::{compound_interest, simple_interest};
 pub use self::interpolation::{lagrange_polynomial_interpolation, linear_interpolation};
 pub use self::interquartile_range::interquartile_range;