feat: add kmp version index_of

Author: Chronostasys

planglib/std/slice.pi

@@ -1,5 +1,6 @@
 pub trait SliceExt<T> {
     fn index_of(sub_arr:[T]) Option<i64>;
+    fn index_of_kmp(sub_arr:[T]) Option<i64>;
     fn len() i64;
     fn slice(start: i64, end: i64) [T];
     fn copy(to:[T], len:i64) Result<()|SliceOutOfIdxErr>;
@@ -9,6 +10,25 @@ pub struct SliceOutOfIdxErr {
 
 }
 
+
+fn arr_next<T:Eq<T>>(arr:[T]) [i64] {
+    let len = arr.len();
+    let next = [0* len];
+    next[0] = -1;
+    let i = 0;
+    let j = -1;
+    while i < len - 1 {
+        if j == -1 || arr[i].eq(&arr[j]) {
+            i = i + 1;
+            j = j + 1;
+            next[i] = j;
+        } else {
+            j = next[j];
+        }
+    }
+    return next;
+}
+
 use core::eq::Eq;
 impl<T:Eq<T>> SliceExt<T> for [T] {
     /// # index_of
@@ -17,6 +37,18 @@ impl<T:Eq<T>> SliceExt<T> for [T] {
     fn index_of(sub_arr:[T])  Option<i64> {
         let len = self.len();
         let sub_len = sub_arr.len();
+
+        // Calculate the expected cost of both algorithms
+        let cost_index_of = len * sub_len/2;
+        let cost_index_of_kmp = len + sub_len;
+
+        // Choose the algorithm with the lower expected cost
+        if cost_index_of_kmp < cost_index_of {
+            return self.index_of_kmp(sub_arr);
+        }
+
+
+
         if sub_len > len || sub_len == 0{
             return None{};
         }
@@ -38,6 +70,31 @@ impl<T:Eq<T>> SliceExt<T> for [T] {
 
     }
 
+
+    fn index_of_kmp(sub_arr:[T]) Option<i64> {
+        let len = self.len();
+        let sub_len = sub_arr.len();
+        if sub_len > len || sub_len == 0{
+            return None{};
+        }
+        let next = arr_next(sub_arr);
+        let i = 0;
+        let j = 0;
+        while i < len {
+            if j == -1 || (*self)[i].eq(&sub_arr[j]) {
+                i = i + 1;
+                j = j + 1;
+            } else {
+                j = next[j];
+            }
+            if j == sub_len {
+                return i - sub_len;
+            }
+        }
+        return None{};
+    }
+    
+
     /// # len
     ///
     /// Get the length of the array.

test/test/std_test.pi

@@ -8,6 +8,9 @@ pub fn test_std() void {
     let re1 =  chars.index_of(subchars);
     panic::assert(re is i64);
     panic::assert((re as i64!) == 2);
+    re = "abfdscdcdcdcde".index_of("cdcde"); // will auto use kmp
+    panic::assert(re is i64);
+    panic::assert((re as i64!) == 9);
 
     panic::assert(re1 is i64);
     panic::assert((re1 as i64!) == 2);