【AtCoder】AGC011 D - Half Reflector

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
#include <set>
#include <cmath>
#include <bitset>
#include <queue>
#define enter putchar(‘\n‘)
#define space putchar(‘ ‘)
//#define ivorysi
#define pb push_back
#define mo 974711
#define pii pair<int,int>
#define mp make_pair
#define fi first
#define se second
#define MAXN 200005
#define eps 1e-12
using namespace std;
typedef long long int64;
typedef double db;
template<class T>
void read(T &res) {
    res = 0;char c = getchar();T f = 1;
    while(c < ‘0‘ || c > ‘9‘) {
    if(c == ‘-‘) f = -1;
    c = getchar();
    }
    while(c >= ‘0‘ && c <= ‘9‘) {
    res = res * 10 - ‘0‘ + c;
    c = getchar();
    }
    res = res * f;
}
template<class T>
void out(T x) {
    if(x < 0) {x = -x;putchar(‘-‘);}
    if(x >= 10) out(x / 10);
    putchar(‘0‘ + x % 10);
}
char s[MAXN];
int N,K,p = 1,num[MAXN],cnt,st;
void Solve() {
    read(N);read(K);
    scanf("%s",s + 1);
    for(int i = 1 ; i <= N ; ++i) num[i] = s[i] - ‘A‘;
    st = num[1];
    while(K--) {
    if(st == 0) {st ^= 1;num[p] ^= 1;}
    else {
        ++p;++cnt;
        st = num[p];
        st ^= (cnt & 1);
    }
    if(p > N) break;
    }
    if(p <= N) {
    for(int i = p ; i <= N ; ++i) putchar(‘A‘ + (num[i] ^ (cnt & 1)));
    int t = N - (N - p + 1),c = (cnt - 1) & 1;
    while(t--) {
        putchar(‘A‘ + c);
        c ^= 1;
    }
    }
    else {
    if((cnt - 1) & 1) {
        for(int i = 1 ; i <= N ; ++i) putchar(‘A‘ + (i & 1));
    }
    else {
        putchar(‘A‘ + (K & 1));
        for(int i = 1 ; i < N ; ++i) putchar(‘A‘ + (i & 1));
    }
    }
    enter;
}
int main() {
#ifdef ivorysi
    freopen("f1.in","r",stdin);
#endif
    Solve();
}