KPLANK - Bán dừa
Tác giả: RR
Ngôn ngữ: C++
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <string>
#include <deque>
#include <complex>
#include <sstream>
#include <iomanip>
#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; i--)
#define REP(i,a) for(int i=0,_a=(a); i<_a; i++)
#define ll long long
#define F first
#define S second
#define PB push_back
#define MP make_pair
using namespace std;
const double PI = acos(-1.0);
int INP,AM;
#define BUFSIZE (1<<10)
char BUF[BUFSIZE+1], *inp=BUF;
#define GETCHAR(INP) { \
if(!*inp) { \
fread(BUF,1,BUFSIZE,stdin); \
inp=BUF; \
} \
INP=*inp++; \
}
#define DIG(a) (((a)>='0')&&((a)<='9'))
#define GN(j) { \
AM=0;\
GETCHAR(INP); while(!DIG(INP) && INP!='-') GETCHAR(INP);\
if (INP=='-') {AM=1;GETCHAR(INP);} \
j=INP-'0'; GETCHAR(INP); \
while(DIG(INP)){j=10*j+(INP-'0');GETCHAR(INP);} \
if (AM) j=-j;\
}
int n, st[1000111], a[1000111], l[1000111], r[1000111], top;
int main() {
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);
GN(n); FOR(i,1,n) GN(a[i]);
top = 0; st[0] = 0;
FOR(i,1,n) {
while (top && a[st[top]] >= a[i]) top--;
l[i] = st[top] + 1;
st[++top] = i;
}
top = 0; st[0] = n+1;
FORD(i,n,1) {
while (top && a[st[top]] >= a[i]) top--;
r[i] = st[top] - 1;
st[++top] = i;
}
int res = 0, u;
FOR(i,1,n) {
u = r[i] - l[i] + 1;
if (u < a[i]) continue;
res = max(res, min(u, a[i]));
}
cout << res;
return 0;
}