保卫方案

保卫方案

用单调栈实现

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
struct node {
	int val;
	long count;
	node(int v, int c = 1) : val(v), count(c) {}
};

int main() {
	ios::sync_with_stdio(false);
	int N;
	while (cin >> N) {
		vector<int> watch(N);
		for (int i = 0; i < N; ++i)
			cin >> watch[i];

		vector<node> v;
		node tmp(watch[0]);

		int max_h = watch[0];
		int max_index = 0;
		for (int i = 1; i < N; ++i) {
			if (watch[i] == watch[i - 1])
				tmp.count++;
			else {
				v.push_back(tmp);
				if (max_h < tmp.val) {
					max_h = tmp.val;
					max_index = v.size() - 1;
				}
				tmp.val = watch[i];
				tmp.count = 1;
			}
		}
		// 最后一个元素
		v.push_back(tmp);
		if (max_h < tmp.val) {
			max_h = tmp.val;
			max_index = v.size() - 1;
		}
		int n = 0;
		long count = 0;
		vector<node> stack;
		for (int i = max_index; n < v.size(); ++n, i = (i + 1) % v.size()) {
			while (stack.size() && v[i].val > stack[stack.size() - 1].val) {
				node & tmp = stack[stack.size() - 1];
				count += tmp.count + tmp.count*(tmp.count - 1) / 2;
				stack.pop_back();
				if (stack.size()) count += tmp.count;
			}

			if (stack.size()) {
				if (v[i].val == stack[stack.size() - 1].val)
					stack[stack.size() - 1].count += v[i].count;
				else
					stack.push_back(v[i]);
			}
			else
				stack.push_back(v[i]);
		}
		while (stack.size()) {
			node & tmp = stack[stack.size() - 1];
			count += tmp.count*(tmp.count - 1) / 2;
			stack.pop_back();
			if (stack.size()) count += 2 * tmp.count;
			if (stack.size() == 1 && stack[stack.size() - 1].count == 1) count -= tmp.count;
		}
		cout << count << endl;
	}
	return 0;
}
Written on April 9, 2018