50093. String Substitution

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char ins[1024];

int match(char* s, char* pattern, int len_s, int len_p, int delta){
    for(int i = 0; i < len_p; i++){
        if(s[i + delta] != pattern[i]) return 0;
    }
    return 1;
}
int get_match(char* s, char* pattern, int len_s, int len_p){
    for(int delta = 0; delta <= len_s - len_p; delta++){
        if(match(s, pattern, len_s, len_p, delta)) return delta;
    }
    return -1;
}
void get_ps(char* ins, char* pattern, char* sub, int* pattern_len, int* sub_len){
    char sep = ins[1];

    int n = 0, m = 0;
    for(int i = 2; ins[i] != sep; i++) pattern[n++] = ins[i];
    pattern[n] = '\0';

    for(int i = n + 3; ins[i] != sep; i++) sub[m++] = ins[i];
    sub[m] = '\0';

    *pattern_len = n, *sub_len = m;
}
void substitute(char* s, int len_s, char* pattern, char* sub, int pattern_len, int sub_len, int delta){
    if(pattern_len >= sub_len){
        for(int i = 0; i < sub_len; i++) s[i + delta] = sub[i];
        for(int i = delta + pattern_len; i <= len_s; i++) s[i - (pattern_len - sub_len)] = s[i];
    }
    else{
        for(int i = len_s; i >= delta + pattern_len; i--) s[i + (sub_len - pattern_len)] = s[i];
        for(int i = 0; i < sub_len; i++) s[i + delta] = sub[i];
    }
}


int main(){
    char s[1024]; scanf("%s", s);
    int len_s = strlen(s);

    while(fgets(ins, 1024, stdin) != NULL){
        if(ins[0] == 'p') printf("%s\n", s);
        else if(ins[0] == 's'){
            char pattern[1024], sub[1024];
            int pattern_len, sub_len;
            get_ps(ins, pattern, sub, &pattern_len, &sub_len);

            int rtv = get_match(s, pattern, len_s, pattern_len);
            if(rtv != -1){
                substitute(s, len_s, pattern, sub, pattern_len, sub_len, rtv);
                len_s += (sub_len - pattern_len);
            }
        }
    }
}