Merge branch 'master' into ref/ds/rmq

DIRECTORY.md

@@ -101,6 +101,8 @@
     * [Subset Generation](https://github.com/TheAlgorithms/Rust/blob/master/src/dynamic_programming/subset_generation.rs)
     * [Trapped Rainwater](https://github.com/TheAlgorithms/Rust/blob/master/src/dynamic_programming/trapped_rainwater.rs)
     * [Word Break](https://github.com/TheAlgorithms/Rust/blob/master/src/dynamic_programming/word_break.rs)
+  * Financial
+    * [Present Value](https://github.com/TheAlgorithms/Rust/blob/master/src/financial/present_value.rs)
   * General
     * [Convex Hull](https://github.com/TheAlgorithms/Rust/blob/master/src/general/convex_hull.rs)
     * [Fisher Yates Shuffle](https://github.com/TheAlgorithms/Rust/blob/master/src/general/fisher_yates_shuffle.rs)

src/dynamic_programming/minimum_cost_path.rs

@@ -1,80 +1,177 @@
-/// Minimum Cost Path via Dynamic Programming
-
-/// Find the minimum cost traced by all possible paths from top left to bottom right in
-/// a given matrix, by allowing only right and down movement
-
-/// For example, in matrix,
-/// [2, 1, 4]
-/// [2, 1, 3]
-/// [3, 2, 1]
-/// The minimum cost path is 7
-
-/// # Arguments:
-///   * `matrix` - The input matrix.
-/// # Complexity
-///   - time complexity: O( rows * columns ),
-///   - space complexity: O( rows * columns )
 use std::cmp::min;
 
-pub fn minimum_cost_path(mut matrix: Vec<Vec<usize>>) -> usize {
-    // Add rows and columns variables for better readability
-    let rows = matrix.len();
-    let columns = matrix[0].len();
+/// Represents possible errors that can occur when calculating the minimum cost path in a matrix.
+#[derive(Debug, PartialEq, Eq)]
+pub enum MatrixError {
+    /// Error indicating that the matrix is empty or has empty rows.
+    EmptyMatrix,
+    /// Error indicating that the matrix is not rectangular in shape.
+    NonRectangularMatrix,
+}
 
-    // Preprocessing the first row
-    for i in 1..columns {
-        matrix[0][i] += matrix[0][i - 1];
+/// Computes the minimum cost path from the top-left to the bottom-right
+/// corner of a matrix, where movement is restricted to right and down directions.
+///
+/// # Arguments
+///
+/// * `matrix` - A 2D vector of positive integers, where each element represents
+///              the cost to step on that cell.
+///
+/// # Returns
+///
+/// * `Ok(usize)` - The minimum path cost to reach the bottom-right corner from
+///   the top-left corner of the matrix.
+/// * `Err(MatrixError)` - An error if the matrix is empty or improperly formatted.
+///
+/// # Complexity
+///
+/// * Time complexity: `O(m * n)`, where `m` is the number of rows
+///   and `n` is the number of columns in the input matrix.
+/// * Space complexity: `O(n)`, as only a single row of cumulative costs
+///   is stored at any time.
+pub fn minimum_cost_path(matrix: Vec<Vec<usize>>) -> Result<usize, MatrixError> {
+    // Check if the matrix is rectangular
+    if !matrix.iter().all(|row| row.len() == matrix[0].len()) {
+        return Err(MatrixError::NonRectangularMatrix);
     }
 
-    // Preprocessing the first column
-    for i in 1..rows {
-        matrix[i][0] += matrix[i - 1][0];
+    // Check if the matrix is empty or contains empty rows
+    if matrix.is_empty() || matrix.iter().all(|row| row.is_empty()) {
+        return Err(MatrixError::EmptyMatrix);
     }
 
-    // Updating path cost for the remaining positions
-    // For each position, cost to reach it from top left is
-    // Sum of value of that position and minimum of upper and left position value
+    // Initialize the first row of the cost vector
+    let mut cost = matrix[0]
+        .iter()
+        .scan(0, |acc, &val| {
+            *acc += val;
+            Some(*acc)
+        })
+        .collect::<Vec<_>>();
 
-    for i in 1..rows {
-        for j in 1..columns {
-            matrix[i][j] += min(matrix[i - 1][j], matrix[i][j - 1]);
+    // Process each row from the second to the last
+    for row in matrix.iter().skip(1) {
+        // Update the first element of cost for this row
+        cost[0] += row[0];
+
+        // Update the rest of the elements in the current row of cost
+        for col in 1..matrix[0].len() {
+            cost[col] = row[col] + min(cost[col - 1], cost[col]);
         }
     }
 
-    // Return cost for bottom right element
-    matrix[rows - 1][columns - 1]
+    // The last element in cost contains the minimum path cost to the bottom-right corner
+    Ok(cost[matrix[0].len() - 1])
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    #[test]
-    fn basic() {
-        // For test case in example
-        let matrix = vec![vec![2, 1, 4], vec![2, 1, 3], vec![3, 2, 1]];
-        assert_eq!(minimum_cost_path(matrix), 7);
-
-        // For a randomly generated matrix
-        let matrix = vec![vec![1, 2, 3], vec![4, 5, 6]];
-        assert_eq!(minimum_cost_path(matrix), 12);
-    }
-
-    #[test]
-    fn one_element_matrix() {
-        let matrix = vec![vec![2]];
-        assert_eq!(minimum_cost_path(matrix), 2);
-    }
-
-    #[test]
-    fn one_row() {
-        let matrix = vec![vec![1, 3, 2, 1, 5]];
-        assert_eq!(minimum_cost_path(matrix), 12);
+    macro_rules! minimum_cost_path_tests {
+        ($($name:ident: $test_case:expr,)*) => {
+            $(
+                #[test]
+                fn $name() {
+                    let (matrix, expected) = $test_case;
+                    assert_eq!(minimum_cost_path(matrix), expected);
+                }
+            )*
+        };
     }
 
-    #[test]
-    fn one_column() {
-        let matrix = vec![vec![1], vec![3], vec![2], vec![1], vec![5]];
-        assert_eq!(minimum_cost_path(matrix), 12);
+    minimum_cost_path_tests! {
+        basic: (
+            vec![
+                vec![2, 1, 4],
+                vec![2, 1, 3],
+                vec![3, 2, 1]
+            ],
+            Ok(7)
+        ),
+        single_element: (
+            vec![
+                vec![5]
+            ],
+            Ok(5)
+        ),
+        single_row: (
+            vec![
+                vec![1, 3, 2, 1, 5]
+            ],
+            Ok(12)
+        ),
+        single_column: (
+            vec![
+                vec![1],
+                vec![3],
+                vec![2],
+                vec![1],
+                vec![5]
+            ],
+            Ok(12)
+        ),
+        large_matrix: (
+            vec![
+                vec![1, 3, 1, 5],
+                vec![2, 1, 4, 2],
+                vec![3, 2, 1, 3],
+                vec![4, 3, 2, 1]
+            ],
+            Ok(10)
+        ),
+        uniform_matrix: (
+            vec![
+                vec![1, 1, 1],
+                vec![1, 1, 1],
+                vec![1, 1, 1]
+            ],
+            Ok(5)
+        ),
+        increasing_values: (
+            vec![
+                vec![1, 2, 3],
+                vec![4, 5, 6],
+                vec![7, 8, 9]
+            ],
+            Ok(21)
+        ),
+        high_cost_path: (
+            vec![
+                vec![1, 100, 1],
+                vec![1, 100, 1],
+                vec![1, 1, 1]
+            ],
+            Ok(5)
+        ),
+        complex_matrix: (
+            vec![
+                vec![5, 9, 6, 8],
+                vec![1, 4, 7, 3],
+                vec![2, 1, 8, 2],
+                vec![3, 6, 9, 4]
+            ],
+            Ok(23)
+        ),
+        empty_matrix: (
+            vec![],
+            Err(MatrixError::EmptyMatrix)
+        ),
+        empty_row: (
+            vec![
+                vec![],
+                vec![],
+                vec![]
+            ],
+            Err(MatrixError::EmptyMatrix)
+        ),
+        non_rectangular: (
+            vec![
+                vec![1, 2, 3],
+                vec![4, 5],
+                vec![6, 7, 8]
+            ],
+            Err(MatrixError::NonRectangularMatrix)
+        ),
     }
 }

src/financial/mod.rs

@@ -0,0 +1,2 @@
+mod present_value;
+pub use present_value::present_value;

src/financial/present_value.rs

@@ -0,0 +1,91 @@
+/// In economics and finance, present value (PV), also known as present discounted value,
+/// is the value of an expected income stream determined as of the date of valuation.
+///
+/// -> Wikipedia reference: https://en.wikipedia.org/wiki/Present_value
+
+#[derive(PartialEq, Eq, Debug)]
+pub enum PresentValueError {
+    NegetiveDiscount,
+    EmptyCashFlow,
+}
+
+pub fn present_value(discount_rate: f64, cash_flows: Vec<f64>) -> Result<f64, PresentValueError> {
+    if discount_rate < 0.0 {
+        return Err(PresentValueError::NegetiveDiscount);
+    }
+    if cash_flows.is_empty() {
+        return Err(PresentValueError::EmptyCashFlow);
+    }
+
+    let present_value = cash_flows
+        .iter()
+        .enumerate()
+        .map(|(i, &cash_flow)| cash_flow / (1.0 + discount_rate).powi(i as i32))
+        .sum::<f64>();
+
+    Ok(round(present_value))
+}
+
+fn round(value: f64) -> f64 {
+    (value * 100.0).round() / 100.0
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    macro_rules! test_present_value {
+        ($($name:ident: $inputs:expr,)*) => {
+            $(
+                #[test]
+                fn $name() {
+                    let ((discount_rate,cash_flows), expected) = $inputs;
+                    assert_eq!(present_value(discount_rate,cash_flows).unwrap(), expected);
+                }
+            )*
+        }
+    }
+
+    macro_rules! test_present_value_Err {
+        ($($name:ident: $inputs:expr,)*) => {
+            $(
+                #[test]
+                fn $name() {
+                    let ((discount_rate,cash_flows), expected) = $inputs;
+                    assert_eq!(present_value(discount_rate,cash_flows).unwrap_err(), expected);
+                }
+            )*
+        }
+    }
+
+    macro_rules! test_round {
+        ($($name:ident: $inputs:expr,)*) => {
+            $(
+                #[test]
+                fn $name() {
+                    let (input, expected) = $inputs;
+                    assert_eq!(round(input), expected);
+                }
+            )*
+        }
+    }
+
+    test_present_value! {
+        general_inputs1:((0.13, vec![10.0, 20.70, -293.0, 297.0]),4.69),
+        general_inputs2:((0.07, vec![-109129.39, 30923.23, 15098.93, 29734.0, 39.0]),-42739.63),
+        general_inputs3:((0.07, vec![109129.39, 30923.23, 15098.93, 29734.0, 39.0]), 175519.15),
+        zero_input:((0.0, vec![109129.39, 30923.23, 15098.93, 29734.0, 39.0]),  184924.55),
+
+    }
+
+    test_present_value_Err! {
+        negative_discount_rate:((-1.0, vec![10.0, 20.70, -293.0, 297.0]), PresentValueError::NegetiveDiscount),
+        empty_cash_flow:((1.0, vec![]), PresentValueError::EmptyCashFlow),
+
+    }
+    test_round! {
+            test1:(0.55434,  0.55),
+            test2:(10.453,  10.45),
+            test3:(1111_f64,  1111_f64),
+    }
+}