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