Add Infix to Postfix Algorithm and Update DIRECTORY.md (TheAlgorithms#541)

Author: cyrixninja

DIRECTORY.md

@@ -44,6 +44,7 @@
     * [Heap](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/heap.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)
     * Probabilistic
       * [Bloom Filter](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/probabilistic/bloom_filter.rs)
       * [Count Min Sketch](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/probabilistic/count_min_sketch.rs)
@@ -55,6 +56,7 @@
     * [Treap](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/treap.rs)
     * [Trie](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/trie.rs)
     * [Union Find](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/union_find.rs)
+    * [Veb Tree](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/veb_tree.rs)
   * Dynamic Programming
     * [Coin Change](https://github.com/TheAlgorithms/Rust/blob/master/src/dynamic_programming/coin_change.rs)
     * [Egg Dropping](https://github.com/TheAlgorithms/Rust/blob/master/src/dynamic_programming/egg_dropping.rs)
@@ -88,6 +90,10 @@
     * [Two Sum](https://github.com/TheAlgorithms/Rust/blob/master/src/general/two_sum.rs)
   * Geometry
     * [Closest Points](https://github.com/TheAlgorithms/Rust/blob/master/src/geometry/closest_points.rs)
+    * [Graham Scan](https://github.com/TheAlgorithms/Rust/blob/master/src/geometry/graham_scan.rs)
+    * [Jarvis Scan](https://github.com/TheAlgorithms/Rust/blob/master/src/geometry/jarvis_scan.rs)
+    * [Point](https://github.com/TheAlgorithms/Rust/blob/master/src/geometry/point.rs)
+    * [Segment](https://github.com/TheAlgorithms/Rust/blob/master/src/geometry/segment.rs)
   * Graph
     * [Astar](https://github.com/TheAlgorithms/Rust/blob/master/src/graph/astar.rs)
     * [Bellman Ford](https://github.com/TheAlgorithms/Rust/blob/master/src/graph/bellman_ford.rs)
@@ -114,6 +120,8 @@
     * [Abs](https://github.com/TheAlgorithms/Rust/blob/master/src/math/abs.rs)
     * [Aliquot Sum](https://github.com/TheAlgorithms/Rust/blob/master/src/math/aliquot_sum.rs)
     * [Amicable Numbers](https://github.com/TheAlgorithms/Rust/blob/master/src/math/amicable_numbers.rs)
+    * [Area Of Polygon](https://github.com/TheAlgorithms/Rust/blob/master/src/math/area_of_polygon.rs)
+    * [Area Under Curve](https://github.com/TheAlgorithms/Rust/blob/master/src/math/area_under_curve.rs)
     * [Armstrong Number](https://github.com/TheAlgorithms/Rust/blob/master/src/math/armstrong_number.rs)
     * [Baby Step Giant Step](https://github.com/TheAlgorithms/Rust/blob/master/src/math/baby_step_giant_step.rs)
     * [Bell Numbers](https://github.com/TheAlgorithms/Rust/blob/master/src/math/bell_numbers.rs)
@@ -149,16 +157,21 @@
     * [Quadratic Residue](https://github.com/TheAlgorithms/Rust/blob/master/src/math/quadratic_residue.rs)
     * [Random](https://github.com/TheAlgorithms/Rust/blob/master/src/math/random.rs)
     * [Sieve Of Eratosthenes](https://github.com/TheAlgorithms/Rust/blob/master/src/math/sieve_of_eratosthenes.rs)
+    * [Sigmoid](https://github.com/TheAlgorithms/Rust/blob/master/src/math/sigmoid.rs)
     * [Signum](https://github.com/TheAlgorithms/Rust/blob/master/src/math/signum.rs)
     * [Simpson Integration](https://github.com/TheAlgorithms/Rust/blob/master/src/math/simpson_integration.rs)
     * [Sine](https://github.com/TheAlgorithms/Rust/blob/master/src/math/sine.rs)
     * [Square Root](https://github.com/TheAlgorithms/Rust/blob/master/src/math/square_root.rs)
     * [Sum Of Digits](https://github.com/TheAlgorithms/Rust/blob/master/src/math/sum_of_digits.rs)
+    * [Tanh](https://github.com/TheAlgorithms/Rust/blob/master/src/math/tanh.rs)
     * [Trial Division](https://github.com/TheAlgorithms/Rust/blob/master/src/math/trial_division.rs)
     * [Zellers Congruence Algorithm](https://github.com/TheAlgorithms/Rust/blob/master/src/math/zellers_congruence_algorithm.rs)
   * Navigation
     * [Bearing](https://github.com/TheAlgorithms/Rust/blob/master/src/navigation/bearing.rs)
     * [Haversine](https://github.com/TheAlgorithms/Rust/blob/master/src/navigation/haversine.rs)
+  * Number Theory
+    * [Totient Function](https://github.com/TheAlgorithms/Rust/blob/master/src/number_theory/compute_totient.rs)
+    * [Kth Factor of N](https://github.com/TheAlgorithms/Rust/blob/master/src/number_theory/kth_factor.rs)
   * Searching
     * [Binary Search](https://github.com/TheAlgorithms/Rust/blob/master/src/searching/binary_search.rs)
     * [Binary Search Recursive](https://github.com/TheAlgorithms/Rust/blob/master/src/searching/binary_search_recursive.rs)
@@ -177,6 +190,7 @@
   * Sorting
     * [Bead Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/bead_sort.rs)
     * [Bitonic Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/bitonic_sort.rs)
+    * [Binary Insertion Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/binary_insertion_sort.rs)
     * [Bogo Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/bogo_sort.rs)
     * [Bubble Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/bubble_sort.rs)
     * [Bucket Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/bucket_sort.rs)
@@ -189,12 +203,14 @@
     * [Gnome Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/gnome_sort.rs)
     * [Heap Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/heap_sort.rs)
     * [Insertion Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/insertion_sort.rs)
+    * [Intro Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/intro_sort.rs)
     * [Merge Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/merge_sort.rs)
     * [Odd Even Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/odd_even_sort.rs)
     * [Pancake Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/pancake_sort.rs)
     * [Patience Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/patience_sort.rs)
     * [Pigeonhole Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/pigeonhole_sort.rs)
     * [Quick Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/quick_sort.rs)
+    * [Quick Sort 3 Ways](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/quick_sort_3_ways.rs)
     * [Radix Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/radix_sort.rs)
     * [Selection Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/selection_sort.rs)
     * [Shell Sort](https://github.com/TheAlgorithms/Rust/blob/master/src/sorting/shell_sort.rs)
@@ -219,5 +235,6 @@
     * [Reverse](https://github.com/TheAlgorithms/Rust/blob/master/src/string/reverse.rs)
     * [Run Length Encoding](https://github.com/TheAlgorithms/Rust/blob/master/src/string/run_length_encoding.rs)
     * [Suffix Array](https://github.com/TheAlgorithms/Rust/blob/master/src/string/suffix_array.rs)
+    * [Suffix Array Manber Myers](https://github.com/TheAlgorithms/Rust/blob/master/src/string/suffix_array_manber_myers.rs)
     * [Suffix Tree](https://github.com/TheAlgorithms/Rust/blob/master/src/string/suffix_tree.rs)
     * [Z Algorithm](https://github.com/TheAlgorithms/Rust/blob/master/src/string/z_algorithm.rs)

src/data_structures/infix_to_postfix.rs

@@ -0,0 +1,76 @@
+// Function to convert infix expression to postfix expression
+fn infix_to_postfix(infix: &str) -> String {
+    let mut postfix = String::new();
+    let mut stack: Vec<char> = Vec::new();
+
+    // Define the precedence of operators
+    let precedence = |op: char| -> i32 {
+        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);
+            }
+            _ => {}
+        }
+    }
+
+    while let Some(top) = stack.pop() {
+        if top == '(' {
+            // If there are unmatched parentheses, it's an error.
+            return "Error: Unmatched parentheses".to_string();
+        }
+        postfix.push(top);
+    }
+
+    postfix
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_infix_to_postfix() {
+        assert_eq!(
+            infix_to_postfix("a-b+c-d*e"),
+            "ab-c+de*-".to_string()
+        );
+        assert_eq!(
+            infix_to_postfix("a*(b+c)+d/(e+f)"),
+            "abc+*def+/+".to_string()
+        );
+        assert_eq!(
+            infix_to_postfix("(a-b+c)*(d+e*f)"),
+            "ab-c+def*+*".to_string()
+        );
+    }
+}