implemented count function

Author: aman-godara

src/stdlib_strings.f90

@@ -12,7 +12,7 @@ module stdlib_strings
 
     public :: strip, chomp
     public :: starts_with, ends_with
-    public :: slice, find, replace_all
+    public :: slice, find, replace_all, count
 
 
     !> Remove leading and trailing whitespace characters.
@@ -93,6 +93,17 @@ module stdlib_strings
         module procedure :: replace_all_char_char_char
     end interface replace_all
 
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> [Specifications](link to the specs - to be completed)
+    !> Version: experimental
+    interface count
+        module procedure :: count_string_string
+        module procedure :: count_string_char
+        module procedure :: count_char_string
+        module procedure :: count_char_char
+    end interface count
+
 contains
 
 
@@ -649,4 +660,87 @@ pure function replace_all_char_char_char(string, pattern, replacement) result(re
 
     end function replace_all_char_char_char
 
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> Returns an integer
+    elemental function count_string_string(string, pattern, consider_overlapping) result(res)
+        type(string_type), intent(in) :: string
+        type(string_type), intent(in) :: pattern
+        logical, intent(in), optional :: consider_overlapping
+        integer :: res
+
+        res = count(char(string), char(pattern), consider_overlapping)
+
+    end function count_string_string
+
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> Returns an integer
+    elemental function count_string_char(string, pattern, consider_overlapping) result(res)
+        type(string_type), intent(in) :: string
+        character(len=*), intent(in) :: pattern
+        logical, intent(in), optional :: consider_overlapping
+        integer :: res
+
+        res = count(char(string), pattern, consider_overlapping)
+
+    end function count_string_char
+
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> Returns an integer
+    elemental function count_char_string(string, pattern, consider_overlapping) result(res)
+        character(len=*), intent(in) :: string
+        type(string_type), intent(in) :: pattern
+        logical, intent(in), optional :: consider_overlapping
+        integer :: res
+
+        res = count(string, char(pattern), consider_overlapping)
+
+    end function count_char_string
+
+    !> Returns the number of times substring 'pattern' has appeared in the
+    !> input string 'string'
+    !> Returns an integer
+    elemental function count_char_char(string, pattern, consider_overlapping) result(res)
+        character(len=*), intent(in) :: string
+        character(len=*), intent(in) :: pattern
+        logical, intent(in), optional :: consider_overlapping
+        integer :: lps_array(len(pattern))
+        integer :: res, s_i, p_i, length_string, length_pattern
+        logical :: consider_overlapping_
+
+        consider_overlapping_ = optval(consider_overlapping, .true.)
+        res = 0
+        length_string = len(string)
+        length_pattern = len(pattern)
+
+        if (length_pattern > 0 .and. length_pattern <= length_string) then
+            lps_array = compute_lps(pattern)
+
+            s_i = 1
+            p_i = 1
+            do while(s_i <= length_string)
+                if (string(s_i:s_i) == pattern(p_i:p_i)) then
+                    if (p_i == length_pattern) then
+                        res = res + 1
+                        if (consider_overlapping_) then
+                            p_i = lps_array(p_i)
+                        else
+                            p_i = 0
+                        end if
+                    end if
+                    s_i = s_i + 1
+                    p_i = p_i + 1
+                else if (p_i > 1) then
+                    p_i = lps_array(p_i - 1) + 1
+                else
+                    s_i = s_i + 1
+                end if
+            end do
+        end if
+    
+    end function count_char_char
+    
+
 end module stdlib_strings