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| #include <iostream>
#include <cstdio>
#include <set>
#include <cstring>
#define maxn 5010
#define maxm 1000010
#define INF 1000000000
#define ll long long
using namespace std;
int n, a[maxn], pre[maxn], suf[maxn];
int f[maxn][maxn];
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
cin >> n;
for (int i = 1; i <= n; ++i) cin >> a[i], a[i] = min(a[i], n + 1);
fill(f[0], f[0] + maxn * maxn, INF); f[0][0] = 0;
for (int i = 0; i < n; ++i) {
fill(pre, pre + maxn, INF);
fill(suf, suf + maxn, INF);
int v = a[i + 1];
for (int j = 0; j <= n; ++j) {
if (f[i][j] == INF) continue;
if (v < j) pre[v] = min(pre[v], f[i][j]);
else if (v == j) {
f[i + 1][v] = min(f[i + 1][v], f[i][j]);
pre[v - 1] = min(pre[v - 1], f[i][j] + 1);
}
else {
f[i + 1][v] = min(f[i + 1][v], f[i][j] + v - j);
pre[j] = min(pre[j], f[i][j] + 1);
suf[j] = min(suf[j], f[i][j] + 1);
}
}
int w = INF;
for (int j = v; ~j; --j) {
w = min(w, pre[j]);
f[i + 1][j] = min(f[i + 1][j], w);
}
w = INF;
for (int j = 0; j <= v; ++j) {
w = min(w + 1, suf[j]);
f[i + 1][j] = min(f[i + 1][j], w);
}
}
int ans = INF;
for (int i = 0; i <= n; ++i) ans = min(ans, f[n][i]);
cout << ans << "\n";
return 0;
}
|