SPOJ PALIN Segmentation Fault

I am trying to solve this problem on SPOJ and I wrote this code:

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long llu;
typedef vector<int> vi;

int vi_cmp(const vi& a, const vi& b);
void palin_vi_inc(vi& a, ll& rt, ll& lt);

int main() {

    int T;
    cin >> T;

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

        string input;
        cin >> input;
        if (cin) {
        vi inp_dig;
        for (char c : input) inp_dig.push_back(c - '0');

        vi res_dig = inp_dig;
        for (size_t j = 0; j < (res_dig.size()) / 2; j++) {
            res_dig[res_dig.size() - j - 1] = res_dig[j];
        }

        ll rt = (res_dig.size() - 1) / 2;
        ll lt = (res_dig.size()) / 2;

        while (vi_cmp(res_dig, inp_dig) != 1) {
            palin_vi_inc(res_dig, rt, lt);
        }

        for (vi::iterator it = res_dig.begin(); it < res_dig.end(); ++it) {
            cout << *it;
        }
        cout << endl;
    }
    }

    return 0;
}

int vi_cmp(const vi& a, const vi& b) {

    if (a.size() > b.size()) return +1;
    if (a.size() < b.size()) return -1;

    for (size_t i = 0; i < a.size(); ++i) {
        if (a[i] > b[i]) return +1;
        if (a[i] < b[i]) return -1;
    }

    return 0;
}

void palin_vi_inc(vi& a, ll& rt, ll& lt) {

    if (rt < 0) {
        a[a.size() - 1] = 1;
        a.insert(a.begin(), 1);
        return;
    }
    else if (a[rt] < 9) {
        a[rt] = a[lt] = a[rt] + 1;
        return;
    }
    else {
        a[rt] = a[lt] = 0;
        rt--;
        lt++;
        palin_vi_inc(a, rt, lt);
        return;
    }
}

and it runs correctly on ideone with my test cases. But when I tried to submit it, it gave me Segmentation Fault aka SIGSEGV. What is the test case that is causing the segmentation fault ?

Here is the link to the problem http://ift.tt/1ocDMWz