题目

输入a b c 三个字符串，判断c是否是a、b中的字符，并且分别按在a、b中的顺序出现在c里

#include 
using namespace std;

// case 0 , nomal
// case 1 , null
// case 2 , a、b重复
// case 3 , a 或 b有叠词
// case 4 ， a、b 字符串逆序

bool foo(char* a, int sa, char* b, int sb,  char* c, int sc) {
    if (nullptr == a || nullptr == b || nullptr == c ) {
        return false;
    }
    if (sa < 0 || sb < 0 || sc < 0) {
        return false;
    }
    if ( sa + sb != sc) {
        return false;
    }
    if (*c != *a && *c != *b) {
        return false;
    }
    if (sa == 0 && sb == 0 && sc == 0) {
        return true;
    }
    if (*a == *b && sa > 0 && sb > 0) {
        bool check = false;
        check |= foo(a+1, sa-1, b, sb, c+1, sc-1);
        check |= foo(a, sa, b+1, sb-1, c+1, sc-1);
        return check;
    } else if (*a == *c && sa > 0) {
        return foo(a+1, sa-1, b, sb, c+1, sc -1);
    } else if (*b == *c && sb > 0) {
        return foo(a, sa, b+1, sb-1, c+1, sc-1);
    }
    return true;
}

int main() {
    cout << "0 foo expect 1:" << foo("",0, "",0, "",0) << endl;
    cout << "1 foo expect 1:" << foo("abc",3, "123",3, "a1b2c3",6) << endl;
    cout << "2 foo expect 0:" << foo("acb",3, "123",3, "a1b2c3",6) << endl;
    cout << "3 foo expect 0:" << foo("acb",3, "123",3, "a1b2b3",6) << endl;
    cout << "4 foo expect 0:" << foo("acc",3, "123",3, "a1b2c3",6) << endl;
    cout << "5 foo expect 1:" << foo("acc",3, "123",3, "acc123",6) << endl;
    cout << "6 foo expect 1:" << foo("acc",3, "1b23",4, "a1cbc23",7) << endl;
    cout << "6 foo expect 0:" << foo("acc",3, "1b23",4, "a1cbc2",6) << endl;
    return 0;
}

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