# Codeforces 464c substitutes in number (efficient + fast power)

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Link: codeforces 464c substitutes in number

Given a string, and the Transformation Operation in N, convert a number into a string, which may be a null string, and finally convert the string into one

Number, modulo 1 E9 + 7.

Solution: The operation is processed in reverse mode. In this way, the Val and Len values of each number are maintained. Val indicates the modulo 1e9 + 7 for the corresponding value, and Len indicates the number of corresponding values.

Bit.

``#include <cstdio>#include <cstring>#include <vector>#include <algorithm>using namespace std;typedef long long ll;const int maxn = 1e5+5;const ll mod = 1e9+7;char s[maxn], o[maxn];int n;ll v[20], l[20];ll pow_mod (ll x, int n) {    ll ret = 1;    while (n) {        if(n&1)            ret = ret * x % mod;        x = x * x % mod;        n >>= 1;    }    return ret;}struct state {    int r;    vector<int> vec;    void set (char* str) {        int len = strlen(str);        r = str[0] - ‘0‘;        vec.clear();        for (int i = 3; i < len; i++) {            if (str[i] >= ‘0‘ && str[i] <= ‘9‘)                vec.push_back(str[i] - ‘0‘);        }    }    void solve () {        ll val = 0, len = 0;        for (int i = 0; i < vec.size(); i++) {            int u = vec[i];            len += l[u];            val = (val * pow_mod(10, l[u]) + v[u]) % mod;            len %= (mod-1);        }        v[r] = val;        l[r] = len;    }}com[maxn];void init () {    for (int i = 0; i < 10; i++) {        v[i] = i;        l[i] = 1;    }    for (int i = 0; i < n; i++) {        scanf("%s", o);        com[i].set(o);    }    for (int i = n - 1; i >= 0; i--) {        int u = com[i].r;        com[i].solve();    }}int main () {    scanf("%s%d", s, &n);    init();    int len = strlen(s);    ll ans = 0;    for (int i = 0; i < len; i++) {        int u = s[i] - ‘0‘;        ans = (ans * pow_mod(10, l[u]) + v[u]) % mod;    }    printf("%lld\n", ans);    return 0;}``

Codeforces 464c substitutes in number (efficient + fast power)

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