PTA 7-29 删除字符串中的子串

https://pintia.cn/problem-sets/14/problems/809
so ugly...

#include <cstdio>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <string.h>
using namespace std;


int main() {
    char a[100], b[99];
    int fl[100];
    for (int i = 0; i < 100; i++) {
        fl[i] = 1;
    }
    
    int cnt = 0; 
    while (1) {
        char c;
        scanf("%c", &c);
        if (c == '\n') {
            a[cnt] = '\0';
            break;
        }
        a[cnt++] = c;
    }
     cnt = 0; 
    while (1) {
        char c;
        scanf("%c", &c);
        if (c == '\n') {
            b[cnt] = '\0';
            break;
        }
        b[cnt++] = c;
    }
    
    //printf("%d ", strlen(b));
    
    bool flag = true;
    while (flag) {
        flag = false;
        for (int i = 0; i < strlen(a); i++) {
            int k = i;
            
            int j = 0;
            
            while (j < strlen(b)) {
                if (!fl[k + j]) {
                    k++;
                    continue;
                }
                if (a[k + j] == b[j])
                    j++;
                else
                    break;
            }
            
            if (j == strlen(b)) {
                flag = true;
                j = 0;
                k = i;
                while (j < strlen(b)) {
                    if (!fl[k + j]) {
                        k++;
                        continue;
                    }
                    if (a[k + j] == b[j]) {
                        fl[k + j] = 0;
                        j++;
                    }
                    else
                        break;
                }
            }
        }
    }
    
    for (int i = 0; i < strlen(a); i++) {
        if (fl[i])
            printf("%c", a[i]);
    }
    printf("\n");
    return 0;
}