I need to use a binary search to recursively find a target string. The function should return a -1 if it is not found and a positive integer if found but it always returns -1. thanks for the help!
int start = 0;
int search;
search = binary_search(strings, target, start, size-1);
if(search == -1)
{
printf("Not in the dataset!");
}
if(search != -1)
{
printf("%s is in the dataset", target);
}
int binary_search(char **strings, char *target, int start_idx, int end_idx)
{
if(end_idx < start_idx)
{
return -1;
}
int middle = ((start_idx + end_idx)/2);
int i;
i = strcmp(target, strings[middle]);
if(i == 0)
{
return middle;
}
if(i < 0)
{
return binary_search(strings, target, start_idx, middle-1);
}
else
{
return binary_search(strings, target, middle+1, end_idx);
}
}
input data:
aden
caden
david
erik
john
mark
matt
mycah
phil
susan
Although binary search is notoriously hard to get right, I don't see any errors in your algorithm as shown. You can still fail (-1) due to various causes that can not be determined based on the information provided.
1) Your source strings list is not actually sorted correctly -- strcmp() uses ASCII comparison, not dictionary comparison, i.e., your source string must be ASCII sorted for bsearch to be valid.
2) Your source strings are not well-formed NUL terminated C strings.
3) The target string does not have an exact match in the source string list. i.e., searching for "bill" will not match "Bill" or "billiard"
Just a note, a recursive bsearch is slower than and uses more memory than a non-recursive solution
Related
So right now my code checks if the sub string is present in the code and returns true or false, I would like to find where these substrings are located in the total string. how can you implement that.
#include <stdio.h>
#include <stdbool.h>
bool checksub(const char *strng,const char *subs){
if (*strng=='\0' && *subs!='\0'){
return false;
}
if (*subs=='\0'){
return true;}
if (*strng==*subs){
return checksub(strng+1,subs+1);
}
return false;
}
bool lsub(char *strng,char *subs){
if (*strng=='\0'){
return false;
}
if (*strng==*subs){
if (checksub(strng,subs)){
return 1;
}
}
return lsub(strng+1,subs);
}
int main(){
printf("%d\n",checksub("ababuu","ab"));
printf("%d\n",checksub("the bed bug bites","bit"));
return 0;
}
First you should get rid of recursion since it's often slow and dangerous, for nothing gained.
A (naive) version of strstr that returns an index rather than a pointer might look like this:
int strstr_index (const char* original, const char* sub)
{
int index = -1;
for(const char* str=original; *str!='\0' && index==-1; str++)
{
for(size_t i=0; str[i]==sub[i] && str[i]!='\0'; i++)
{
if(sub[i+1] == '\0')
{
index = (int)(str - original);
break;
}
}
}
return index;
}
This returns -1 if not found, otherwise an index.
It iterates across the string one character at a time.
When a character match with the sub string is found, it starts executing the inner loop as well.
If the inner loop continues to find matches all the way to the end of the sub string, then we found a match.
The index can be obtained by pointer arithmetic: the start address of the found sub string minus the start of the string. The result of that subtraction is strictly speaking a special integer type called ptrdiff_t, but I used int to simplify the example.
I'm given a task to write a program that checks a piece of code, maximum of 20 lines of code, when the program runs you type in a function name, number of lines of code and type in the codes.
It's meant to search in the code and return if the function name you entered is a Library Function or User Defined Function or No Function if it doesn't find it, the code I've written is below, it doesn't work because I made mistakes and I've been trying to fix it but can't seem to figure it out, and I tried debugging to see where I made mistake, and I figured that in the function SearchRealisation it returns an error that
Run-Time Check Failure #2 - Stack around the variable 'buff' was
corrupted.
This program sample returns Library function instead of user defined function
type the function name: addition
Get count string in code: 9
int addition(int num1, int num2)
{
int result = num1 + num2; //trial
return result;
}
int main()
{
addition(8, 9);
}
Output is Library Function but correct output should be User Defined Function since it was defined in the code
void InputText(int length, char Text[MAX_STRINGS][MAX_COLUMNS])
{
//Repeat by Count String
gets_s(Text[0]);
for (int i = 0; i < length; i++)
gets_s(Text[i]);
//Output a string (starting with � zero and ending with Count String-1)
}
void OutMesseg(int param)
{
//Display one of three messages according to the parameter
if (param == -2)
printf("%s", "user defined function");
else if (param == -1)
printf("%s", "no function");
else
printf("%s", "library function");
}
char* DeleteComentsInString(char Text[MAX_STRINGS], char New[MAX_STRINGS])
{
char* a = strstr(Text, "//");
int len = strlen(Text);
if (a != NULL) len -= strlen(a);
strncpy(New, Text, len);
New[len] = '\0';
return New;
}
bool IsTypeC(char Word[MAX_STRINGS])
{
char ctype[6][MAX_STRINGS] =
{
"int",
"bool",
"char",
"float",
"double",
"void"
};
for (int i = 0; i < 6; i++)
{
if (strstr(Word, ctype[i]) != 0)
return true;
}
return false;
}
int SearchRealisation(int length, char Text[MAX_STRINGS][MAX_COLUMNS], int index_fanc, int& end)
{
int count = 0;
int start = -1;
end = -1;
char buff[MAX_STRINGS];
//Find first {
for (int i = index_fanc + 1; i < length && !count; i++)
{
if (strstr(DeleteComentsInString(Text[i], buff), "{") != NULL)
{
count++;
start = i;
}
}
//find last }
for (int i = start + 1; i < length && count; i++)
{
if (strstr(DeleteComentsInString(Text[i], buff), "{") != NULL)
count++;
else if (strstr(DeleteComentsInString(Text[i], buff), "}") != NULL)
count--;
if (!count)
end = i;
}
if (end == -1)
start = -1;
else
return start;
}
int SearchFunction(int length, char Text[MAX_STRINGS][MAX_COLUMNS], char FunctionName[MAX_COLUMNS], int& end)
{
//bool flag = false;
char commentDel[120];
int in;
for (int i = 0; i < length; ++i)
{
DeleteComentsInString(Text[i], commentDel);
if (strstr(commentDel, FunctionName) != NULL)
{
in = strlen(commentDel) - strlen(strstr(commentDel, FunctionName));
if ((in == 0 || (in != 0 && commentDel[in - 1] == ' ')) && (commentDel[in + strlen(FunctionName)] == ' ' || commentDel[in + strlen(FunctionName)] == '(') && strstr(commentDel, ";") == NULL)
{
return SearchRealisation(length, Text, i, end);
}
}
}
end = -1;
return -1;
}
int SearchResult(int length, char Text[MAX_STRINGS][MAX_COLUMNS], char FunctionName[MAX_COLUMNS])
{
int index;
int end;
int start = SearchFunction(length, Text, FunctionName, end);
if (start == -1)
return -1;
index = SearchFunction(length, Text, FunctionName, end);
if (index < 0)
return -2;
return index;
}
int findFunction(char string[MAX_STRINGS][MAX_COLUMNS], char* functName, int M)
{
return 0;
}
int main()
{
int length = 0;
char Code[MAX_STRINGS][MAX_COLUMNS] = { 0 };
char FunctionName[MAX_COLUMNS];
//char ConstantName[MAX_STRINGS];
printf("type the function name: ");
scanf("%s", &FunctionName);
printf("Get count string in code: ");
scanf("%d", &length);
InputText(length, Code);
printf("\n");
OutMesseg(SearchResult(length, Code, FunctionName));
return 0;
}
Well, you have been given a very difficult task:
There's no way to check this, as functions are resolved by a dynamic process that depends on your filesystem state, which is not available at runtime, after you have already compiled your program.
How do you distinguish a function that is compiled in a separate (but user defined) compilation unit from a system defined function? (e.g. double log(double);) that is defined in a math library? There is no way: the linker gets both from a different place (in the first case it gets it from the place you compiled the separate module, in the system case it gets it from a common library directory that has all the system related functions), but you don't have that information available at runtime).
In order to do this task feasible, you'd at least have the full set of source code files of your program. Preprocess them with the cpp(1) preprocessor (so you bypass all the macro expansion invocations) and then check for all function calls in the source code that are not provided in the full set of sources you have. This is quite similar to what the linker does. After compilation, the compiler leaves an object file with the compiled code, and a symbol table that identifies all the unresolved identifiers, and more important all the provided identifiers from this module. The linker then goes on all your modules trying to solve the unknowns, and for each that it doesn't have a solution in your code, it goes to the library directory to search for it. If it doesn't find it in either one, it fails telling you something is wrong.
In my opinion, you have been given a trap task, as the C language preprocess its input (this is something you should do, as many functions are hidden in the internals of macro bodies), then parse the code (for this, you need to write a C parser, which is no trivial task) to select which identifiers are defined in your code and which aren't. Finally you need to check all the calls you do in the code to divide the set in two groups, calls that are defined (and implemented) in your code, and calls that aren't (implemented, all the calls the compiler needs must be defined with some kind of prototype).
It's my opinion, but you have not a simple task, solvable in a short program (of perhaps one hundred lines) but a huge one.
Thanks a lot to everyone that answered I came up with a way to search the code for function definition and thereby return a value if its defined or not, or not even found, might not be the best solution to the task but works so far
I am using bitwise operators to shift the binary value of shorts within a linked list. The function is recursive and after an arbitrary number of occurrences, my right shift seems to affect the value of a short in the next link despite me not pointing to this link at all at this point of the function. Here is my code :
static void move_right(t_tetri *piece) {
int i;
i = 0;
piece->x_offset++;
while (i < piece->height) {
piece->shape[i] = piece->shape[i] >> 1;
i++;
}
}
int ft_solve(t_map *map, t_tetri *list) {
if (list == NULL) return (1);
while (list->y_offset + list->height <= map->size) {
while (list->x_offset + list->width <= map->size) {
if (put_tetri(map, list)) {
set_piece(map, list);
if (ft_solve(map, list->next)) return (1);
else unset_piece(map, list);
}
move_right(list);
}
reset_piece(list);
}
list->y_offset = 0;
return (0);
}
piece->shape is an array containing 4 short but I'm mostly concerned about the first of these here. In certain cases (not all) when I go through the move_right function the value of piece->next->shape[0] is shifted in the same way, which poses a big problem for the next recursion of ft_solve.
Would anyone have any idea?
I can post more of my code if necessary, I'm not really used to ask questions here so if you need more information I'm ready to add it.
I am working on a program to check if a particular string is present in the given string: that is if one string is sub string of another string.
For example:
1)String: YoungPeople --> Substring to be checked: ungPeo
The output should return true.
2)String: Hello How are You? --> Substring to be checked: l*are
The output should return true.
I have used the naive based searching algorithm and it works perfectly fine for the first input.
But I am having trouble in the second kind of input where the asterisk(*) is present which should be treated as a regular expression: i.e. matches zero or more characters.
How should I check for the sub string having an * sign?
Should I try to use the same naive algorithm for searching the character before * and for the string after it? Or is there a better approach to solve this problem?
How should i check for the sub string having an * sign?
Upon reading a *, you need to try 1-2 below.
... use the same naive algorithm for searching ... is there a better approach ...?*
There are better methods. A recursive one follows.
[Edit note: 6/10 found/fixed bug]
As you progress through the string, use recursion to check the rest of the string.
The * simple allows for 2 candidate paths:
1) advance the str
2) advance the substr
Else a matching char allows advancing both.
// StarCompare() helper function
bool StarCmp(const char *str, const char *pat) {
if (*pat == '\0') return 1;
if (*pat == '*') {
if (*str) {
// advance str and use the * again
if (StarCmp(str + 1, pat)) return 1;
}
// let * match nothing and advacne to the next pattern
return StarCmp(str, pat + 1);
}
if (*pat == *str) {
return StarCmp(str + 1, pat + 1);
}
return 0;
}
bool StarCompare(const char *str, const char *pat) {
if (!str || !pat) return 0;
do {
if (StarCmp(str, pat)) return 1;
} while (*str++);
return 0;
}
[Edit Test code in previous version]
The GNU Regex Library seems like what you are looking for. If you are not familiar with regular expression, check this site.
Here is what you have to do:
Split the search string by the * character
Look for each of the parts (in the correct order) in the string you are searching
Alternatively, you can use regexes as other people have suggested.
A good place to look for a well-written implementation of glob matching would be the bash sources. But here's a simple recursive implementation that works:
#include <assert.h>
int
_glob_match(char * pattern, char * str)
{
if (!*pattern) return 1;
if (!*str) return 0;
if (*pattern == '*') return match_any_tail(pattern + 1, str);
if (*pattern != *str) return 0;
else return _glob_match(pattern + 1, str + 1);
}
int
match_any_tail(char * pattern, char * str)
{
for (; *str; str++)
if (_glob_match(pattern, str))
return 1;
return 0;
}
int glob_match(char * pattern, char * str)
{
return match_any_tail (pattern, str);
}
void
main()
{
assert(glob_match("ungPeo", "YoungPeople"));
assert(glob_match("l*are", "Hello How are You?"));
}
I am trying (and having trouble) to write a program (In C) that accepts a string in the command line (eg. $ test.out "This is a string") and looks through the string to find verbs (and nouns, but if I figure out verbs, I can do nouns on my own).
A list of aplphabetically sorted verbs is given in the file lexicon.h, and is what I am supposed to use as my dictionary.
I know how to accept the string from the command line and use that input to create an array of strings, each string itself being a separate word, and I already have a working program that can do that, and that I hope to use part of for this one.
I am supposed to create a function called binary_search(...stuffgoeshere...) and use that to search through the lexicon file and find the verb.
I would like some suggestions or guidance on how to create a function (binary_search) that can check to see if an already separated word matches any on the list in lexicon.h. I do not want someone to just write an answer, I would like to know why you are suggesting what you do. Hopefully I can learn something fun out of this!
I know it's messy, but this is what I have so far.
Also note that lexicon's verb array has 637 values (as seen when I make int size = 637)
This program does not compile anymore, as I have not yet figured out how to make the binary_search function work yet. I am trying to modify a binary search function used in an example for class, however, that one sorted numbers in a text file, not strings of characters.
If there is anything else I should include, let me know. Thank you for your help!
#include <stdio.h>
#include <string.h>
#include "lexicon.h"
int binary_search(char word[], char verbs[][], int size);
int
main(int argc, char*argv[])
{
char word[80];
char str[80],
args[80][80];
int counter = 0,
a = 0,
i = 0,
index = 0,
t = 0;
while(str[a] != '\0')
{
if(str[a] == ' ')
{
args[index][i] = '\0';
i = 0;
a++;
index ++;
counter ++;
}
args[index][i++] = str[a++];
}
args[index][i] = '\0';
counter = counter + 1;
printf("\nThe verbs were: ");
int verbposition= -1;
int size = 637;
while(t<counter)
{
strcpy(word, args[t]);
verbposition = binary_search(word, verbs, size);
if(verbposition > -1)
printf("%s", args[t]);
t++;
}
return 0;
}
int
binary_search(char word[], char &verbs[][], int size)
{
int bottom = 0,
top = size - 1,
found = 0,
middle;
while(bottom <= top && !found)
{
middle = (bottom + top) / 2;
if(strcmp(word, verbs[middle]))
{
found = 1;
return = middle;
}
if(strcmp(word, verbs[middle]) > 0)
{
top = middle - 1;
}
else
bottom = middle + 1;
}
return -1;
}
You are on the right track. I would highly suggest you to use print statements as you will have a clear idea of where you are going wrong.