2452.cpp

#include <iostream>
#include <vector>
#include <list>
#include <map>
//#include <unordered_map>
#include <algorithm>
#include <string>
#include <memory>  
#include <cstring>
#include <stack>
using namespace std;

#include <stdio.h>
#include <stdlib.h>

const int MAXN = 50000;

int s[MAXN + 1];
int r[MAXN + 1]; //first index of smaller element on the right
int m[MAXN + 1]; // index of largest element in [current, r[current])

int main() {
  while (true) {
    int n;
    if(scanf("%d", &n) != 1) break;;
    for (int i = 0; i < n; ++i) {
      scanf("%d", s + i);
    }
    s[n] = -1;
    r[n] = n;
    m[n] = n;
    int ret = -1;
    for (int i = n - 1; i >= 0; --i) {
      int j = i + 1;
      m[i] = i;
      while(s[j] > s[i]) {
        m[i] = s[m[i]] > s[m[j]] ? m[i] : m[j];
        j = r[j];
      }
      r[i] = j;
      ret = max(ret, m[i] - i);
    }
    cout << (ret ? ret : -1) << endl;
  }
  return 0;
}