Merge pull request #73 from ghimiresdp/feature/longest-substring

Dynamic Programming: Longest substring length without duplicates

Author: ghimiresdp

README.md

@@ -139,6 +139,7 @@ cargo test --bin huffman
 7. [Coin Change Problem](problem-solving/src/dp/coin_change.rs) `cargo run --bin coin_change`
 8. [Palindrome Partition](problem-solving/src/dp/palindrome_partition.rs) `cargo run --bin palindrome_partition`
 9. [Find Nth distinct number](problem-solving/src/dp/nth-distinct-number.rs) `cargo run --bin nth-distinct-number`
+10. [Find the length of the longest substring without duplicates](problem-solving/src/dp/longest-substring.rs) `cargo run --bin longest-substring`
 
 ## [5. Advanced Concepts](advanced/README.md)
 

problem-solving/Cargo.toml

@@ -77,3 +77,7 @@ path = 'src/dp/palindrome_partition.rs'
 [[bin]]
 name = 'nth-distinct-number'
 path = 'src/dp/nth-distinct-number.rs'
+
+[[bin]]
+name = 'longest-substring'
+path = 'src/dp/longest-substring.rs'

problem-solving/README.md

@@ -24,3 +24,4 @@
 7. [Coin Change Problem](src/dp/coin_change.rs) `cargo run --bin coin_change`
 8. [Palindrome Partition](src/dp/palindrome_partition.rs) `cargo run --bin palindrome_partition`
 9. [Find Nth distinct number](src/dp/nth-distinct-number.rs) `cargo run --bin nth-distinct-number`
+10. [Find the length of the longest substring without duplicates](src/dp/longest-substring.rs) `cargo run --bin longest-substring`

problem-solving/src/dp/longest-substring.rs

@@ -0,0 +1,69 @@
+//! # Longest Substring without duplicates
+//!
+//! Given a string `s`, find the length of the longest substring without
+//! duplicate characters.
+//!
+//! Here, we check if the duplicate exists using the sliding window.
+//!
+//! we start with the hashmap that stores the character, and it's occurrence
+//! index. if the duplicate is found, left index of that character is moved
+//! so that the starting point of the count will be from that index + 1.
+//!
+//! at the end of the loop, we check if we achieved max length by comparing prev
+//! max length, and updating it.
+
+use std::{cmp::max, collections::HashMap};
+
+fn length_of_longest_substring(string: String) -> usize {
+    // return the length of string if the length is 0 or 1 since it has unique elements
+    if string.len() < 2 {
+        return string.len();
+    }
+
+    let mut left = 0;
+    let mut max_len = 0;
+    let mut char_map: HashMap<char, usize> = HashMap::new();
+
+    for (right, char) in string.chars().enumerate() {
+        if let Some(&index) = char_map.get(&char) {
+            if index >= left {
+                left = index + 1;
+            }
+        }
+        char_map.insert(char, right);
+        max_len = max(max_len, right - left + 1);
+        // TODO: uncomment to see assigned values
+        // println!("character: {char}, left: {left}, right: {right}, max_len: {max_len}");
+    }
+    return max_len;
+}
+fn main() {
+    let length = length_of_longest_substring("abcabcbb".to_owned());
+    println!("length_of_the_longest_substring: {length}");
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::length_of_longest_substring;
+
+    #[test]
+    fn empty_string() {
+        assert_eq!(length_of_longest_substring("".to_owned()), 0);
+    }
+    #[test]
+    fn single_item() {
+        assert_eq!(length_of_longest_substring("a".to_owned()), 1);
+    }
+    #[test]
+    fn two_items() {
+        assert_eq!(length_of_longest_substring("au".to_owned()), 2);
+    }
+    #[test]
+    fn test_for_correctness() {
+        assert_eq!(length_of_longest_substring("abcabcbb".to_owned()), 3);
+        assert_eq!(length_of_longest_substring("bbbbb".to_owned()), 1);
+        assert_eq!(length_of_longest_substring("bbbabb".to_owned()), 2);
+        assert_eq!(length_of_longest_substring("pwwkew".to_owned()), 3);
+        assert_eq!(length_of_longest_substring("abcbcad".to_owned()), 4);
+    }
+}