Add longest common substring (TheAlgorithms#410)

Author: RohitSingh107

src/dynamic_programming/longest_common_substring.rs

@@ -0,0 +1,106 @@
+// Longest common substring via Dynamic Programming
+// longest_common_substring(a, b) returns the length of longest common substring between the strings a and b.
+pub fn longest_common_substring(text1: String, text2: String) -> i32 {
+    let m = text1.len();
+    let n = text2.len();
+
+    let t1 = text1.as_bytes();
+    let t2 = text2.as_bytes();
+
+    // BottomUp Tabulation
+    let mut dp = vec![vec![0; n + 1]; m + 1];
+    let mut ans = 0;
+    for i in 1..=m {
+        for j in 1..=n {
+            if i == 0 || j == 0 {
+                dp[i][j] = 0;
+                continue;
+            }
+            if t1[i - 1] == t2[j - 1] {
+                dp[i][j] = 1 + dp[i - 1][j - 1];
+                ans = std::cmp::max(ans, dp[i][j]);
+            }
+        }
+    }
+
+    ans
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test1() {
+        assert_eq!(
+            longest_common_substring(String::from(""), String::from("")),
+            0
+        );
+    }
+    #[test]
+    fn test2() {
+        assert_eq!(
+            longest_common_substring(String::from("a"), String::from("")),
+            0
+        );
+    }
+    #[test]
+    fn test3() {
+        assert_eq!(
+            longest_common_substring(String::from(""), String::from("a")),
+            0
+        );
+    }
+    #[test]
+    fn test4() {
+        assert_eq!(
+            longest_common_substring(String::from("a"), String::from("a")),
+            1
+        );
+    }
+    #[test]
+    fn test5() {
+        assert_eq!(
+            longest_common_substring(String::from("abcdef"), String::from("bcd")),
+            3
+        );
+    }
+    #[test]
+    fn test6() {
+        assert_eq!(
+            longest_common_substring(String::from("abcdef"), String::from("xabded")),
+            2
+        );
+    }
+    #[test]
+    fn test7() {
+        assert_eq!(
+            longest_common_substring(String::from("GeeksforGeeks"), String::from("GeeksQuiz")),
+            5
+        );
+    }
+    #[test]
+    fn test8() {
+        assert_eq!(
+            longest_common_substring(String::from("abcdxyz"), String::from("xyzabcd")),
+            4
+        );
+    }
+    #[test]
+    fn test9() {
+        assert_eq!(
+            longest_common_substring(String::from("zxabcdezy"), String::from("yzabcdezx")),
+            6
+        );
+    }
+    #[test]
+    fn test10() {
+        assert_eq!(
+            longest_common_substring(
+                String::from("OldSite:GeeksforGeeks.org"),
+                String::from("NewSite:GeeksQuiz.com")
+            ),
+            10
+        );
+    }
+}

src/dynamic_programming/mod.rs

@@ -5,6 +5,7 @@ mod fibonacci;
 mod is_subsequence;
 mod knapsack;
 mod longest_common_subsequence;
+mod longest_common_substring;
 mod longest_continuous_increasing_subsequence;
 mod longest_increasing_subsequence;
 mod maximal_square;
@@ -23,6 +24,7 @@ pub use self::fibonacci::recursive_fibonacci;
 pub use self::is_subsequence::is_subsequence;
 pub use self::knapsack::knapsack;
 pub use self::longest_common_subsequence::longest_common_subsequence;
+pub use self::longest_common_substring::longest_common_substring;
 pub use self::longest_continuous_increasing_subsequence::longest_continuous_increasing_subsequence;
 pub use self::longest_increasing_subsequence::longest_increasing_subsequence;
 pub use self::maximal_square::maximal_square;