【LOJ6404】「ICPC World Finals 2018」逗号播撒机

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【题目链接】

• 点击打开链接

【思路要点】

• 将每一种单词的前，后方抽象为一个点，相邻的位置中间连边，搜索所有联通块即可。
• 时间复杂度 $O(NLogN)$ 。

【代码】

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 1e6 + 5;
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
template <typename T> void chkmax(T &x, T y) {x = max(x, y); }
template <typename T> void chkmin(T &x, T y) {x = min(x, y); } 
template <typename T> void read(T &x) {
	x = 0; int f = 1;
	char c = getchar();
	for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
	for (; isdigit(c); c = getchar()) x = x * 10 + c - '0';
	x *= f;
}
template <typename T> void write(T x) {
	if (x < 0) x = -x, putchar('-');
	if (x > 9) write(x / 10);
	putchar(x % 10 + '0');
}
template <typename T> void writeln(T x) {
	write(x);
	puts("");
}
int n, tot, num[MAXN];
string reals[MAXN];
map <string, int> home;
bool stop[MAXN], comma[MAXN]; 
bool Front[MAXN], Back[MAXN];
vector <int> bf[MAXN], fb[MAXN];
void workf(int pos);
void workb(int pos) {
	if (Back[pos]) return;
	Back[pos] = true;
	for (auto x : bf[pos])
		workf(x); 
}
void workf(int pos) {
	if (Front[pos]) return;
	Front[pos] = true;
	for (auto x : fb[pos])
		workb(x);
}
int main() {
	string tmp;
	while (cin >> tmp) {
		n++;
		if (tmp.back() == '.') {
			tmp.pop_back();
			stop[n] = true;
		}
		if (tmp.back() == ',') {
			tmp.pop_back();
			comma[n] = true;
		}
		if (!home.count(tmp)) {
			home[tmp] = ++tot;
			reals[tot] = tmp;
		}
		num[n] = home[tmp];
	}
	for (int i = 1; i <= n - 1; i++)
		if (!stop[i]) {
			bf[num[i]].push_back(num[i + 1]);
			fb[num[i + 1]].push_back(num[i]);
		}
	for (int i = 1; i <= n - 1; i++)
		if (comma[i]) {
			workb(num[i]);
			workf(num[i + 1]);
		}
	for (int i = 1; i <= n; i++) {
		cout << reals[num[i]];
		if (stop[i]) cout << '.';
		else if (Back[num[i]]) cout << ',';
		cout << ' ';
	}
	return 0;
}