PAT 1024 Palindromic Number

#include <cstdio>

#include <iostream>

#include <cstdlib>

#include <algorithm>



using namespace std;



void print(vector<char> &num) {

    int len = num.size();

    bool value_begin = false;

    for (int i=0; i<len; i++) {

        if (!value_begin && num[i] == 0) continue; // skip leading zeros;

        value_begin = true;

        printf("%d", num[i]);

    }

    if (!value_begin) {         // totally zero

        printf("0");

    }

}



vector<char> num2vec(long long num) {

    vector<char> ret;



    while (num) {

        ret.push_back(num % 10);

        num /= 10;

    }

    reverse(ret.begin(), ret.end());

    return ret;

}



vector<char> add(vector<char> &a, vector<char> &b) {

    vector<char> ret;

    int alen = a.size();

    int blen = b.size();

    int carry= 0;

    while (alen > 0 && blen > 0) {

        int d = carry + a[--alen] + b[--blen];

        carry = d / 10;

        d = d % 10;

        ret.push_back(d);

    }

    

    while (alen > 0) {

        int d = carry + a[--alen];

        carry = d / 10;

        d = d % 10;

        ret.push_back(d);

    }

    while (blen > 0) {

        int d = carry + b[--blen];

        carry = d / 10;

        d = d % 10;

        ret.push_back(d);

    }

    if (carry) ret.push_back(1);

    reverse(ret.begin(), ret.end());

    return ret;

}



vector<char> pal(vector<char> &num) {

    vector<char> ret = num;

    reverse(ret.begin(), ret.end());

    return ret;

}



bool is_pal(vector<char> &num) {

    int len = num.size();

    int p = 0, q = len - 1;

    while (p < q) {

        if (num[p] != num[q]) break;

        ++p, --q;

    }

    return p >= q;

}



int main() {

    long long n = 0, k = 0, i = 0;

    scanf("%ld%ld", &n, &k);

    vector<char> num = num2vec(n);

    for (i=0; i<k; i++) {

        if (is_pal(num)) {

            break;

        }

        vector<char> pnum = pal(num);

        vector<char> tnum = add(pnum, num);

        swap(num, tnum);

    }

    print(num);

    printf("\n%d", i);

    return 0;

}

要注意数值范围，非常喜欢在这种地方搞你一下