From 8669be393e6a6d725276d325b5057c6797c8ebd6 Mon Sep 17 00:00:00 2001
From: Truong Nhan Nguyen <nhantruongnguyen123@gmail.com>
Date: Fri, 27 Sep 2024 21:24:34 +0700
Subject: [PATCH] ref: refactor is subsequence implemenation

---
 src/dynamic_programming/is_subsequence.rs | 78 +++++++++++++++++------
 1 file changed, 58 insertions(+), 20 deletions(-)

diff --git a/src/dynamic_programming/is_subsequence.rs b/src/dynamic_programming/is_subsequence.rs
index 07950fd4519..22b43c387b1 100644
--- a/src/dynamic_programming/is_subsequence.rs
+++ b/src/dynamic_programming/is_subsequence.rs
@@ -1,33 +1,71 @@
-// Given two strings str1 and str2, return true if str1 is a subsequence of str2, or false otherwise.
-// A subsequence of a string is a new string that is formed from the original string
-// by deleting some (can be none) of the characters without disturbing the relative
-// positions of the remaining characters.
-// (i.e., "ace" is a subsequence of "abcde" while "aec" is not).
-pub fn is_subsequence(str1: &str, str2: &str) -> bool {
-    let mut it1 = 0;
-    let mut it2 = 0;
+//! A module for checking if one string is a subsequence of another string.
+//!
+//! A subsequence is formed by deleting some (can be none) of the characters
+//! from the original string without disturbing the relative positions of the
+//! remaining characters. This module provides a function to determine if
+//! a given string is a subsequence of another string.
 
-    let byte1 = str1.as_bytes();
-    let byte2 = str2.as_bytes();
+/// Checks if `sub` is a subsequence of `main`.
+///
+/// # Arguments
+///
+/// * `sub` - A string slice that may be a subsequence.
+/// * `main` - A string slice that is checked against.
+///
+/// # Returns
+///
+/// Returns `true` if `sub` is a subsequence of `main`, otherwise returns `false`.
+pub fn is_subsequence(sub: &str, main: &str) -> bool {
+    let mut sub_iter = sub.chars().peekable();
+    let mut main_iter = main.chars();
 
-    while it1 < str1.len() && it2 < str2.len() {
-        if byte1[it1] == byte2[it2] {
-            it1 += 1;
+    while let Some(&sub_char) = sub_iter.peek() {
+        match main_iter.next() {
+            Some(main_char) if main_char == sub_char => {
+                sub_iter.next();
+            }
+            None => return false,
+            _ => {}
         }
-
-        it2 += 1;
     }
 
-    it1 == str1.len()
+    true
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    #[test]
-    fn test() {
-        assert!(is_subsequence("abc", "ahbgdc"));
-        assert!(!is_subsequence("axc", "ahbgdc"));
+    macro_rules! subsequence_tests {
+        ($($name:ident: $test_case:expr,)*) => {
+            $(
+                #[test]
+                fn $name() {
+                    let (sub, main, expected) = $test_case;
+                    assert_eq!(is_subsequence(sub, main), expected);
+                }
+            )*
+        };
+    }
+
+    subsequence_tests! {
+        test_empty_subsequence: ("", "ahbgdc", true),
+        test_empty_strings: ("", "", true),
+        test_non_empty_sub_empty_main: ("abc", "", false),
+        test_subsequence_found: ("abc", "ahbgdc", true),
+        test_subsequence_not_found: ("axc", "ahbgdc", false),
+        test_longer_sub: ("abcd", "abc", false),
+        test_single_character_match: ("a", "ahbgdc", true),
+        test_single_character_not_match: ("x", "ahbgdc", false),
+        test_subsequence_at_start: ("abc", "abchello", true),
+        test_subsequence_at_end: ("cde", "abcde", true),
+        test_same_characters: ("aaa", "aaaaa", true),
+        test_interspersed_subsequence: ("ace", "abcde", true),
+        test_different_chars_in_subsequence: ("aceg", "abcdef", false),
+        test_single_character_in_main_not_match: ("a", "b", false),
+        test_single_character_in_main_match: ("b", "b", true),
+        test_subsequence_with_special_chars: ("a1!c", "a1!bcd", true),
+        test_case_sensitive: ("aBc", "abc", false),
+        test_subsequence_with_whitespace: ("hello world", "h e l l o   w o r l d", true),
     }
 }