4654. 消除游戏

 4654. 消除游戏 - AcWing题库

#include <iostream>
#include <vector>
#include <cstring>
using namespace std;

const int N = 1e6 + 10;
char s[N];
int l[N], r[N];
vector<int> v, p;
bool st[N];
void ins(int i) {
	if (st[i]) return;
	st[i] = true;
	p.push_back(i);
	return;
}
void fun() {
	p.clear();
	for (int i : v) {
		int a = l[i], b = i, c = r[i];
		if (s[a] == s[b] && s[b] != s[c] && s[c] != '_') {
			ins(b), ins(c);
		}
		else if (s[a] != s[b] && s[b] == s[c] && s[a] != '_') {
			ins(a), ins(b);
		}
	}
	return;
}
int main() {
	cin >> s + 1;
	int n = strlen(s + 1);
	s[0] = s[n + 1] = '_';
	for (int i = 1; i <= n; i++) {
		l[i] = i - 1, r[i] = i + 1;
		v.push_back(i);
	}
	r[0] = 1, l[n + 1] = n;
	while (true) {
		fun();
		if (p.empty()) break;
		v.clear();
		for (int i : p) {
			int a = l[i], b = i, c = r[i];
			if (!st[a] && a && (v.empty() || v.back() != a)) v.push_back(a);
			if (!st[c] && c != n + 1) v.push_back(c);
			r[a] = c, l[c] = a;
		}
	}
	if (r[0] == n + 1) puts("EMPTY");
	else {
		for (int i = r[0]; i != n + 1; i = r[i]) {
			cout << s[i];
		}
	}
	return 0;
}