AtCoder Regular Contest 189 (Div. 2)

A

计数

B

折叠差不变

D

观察性质暴力

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define endl '\n'
#define LL long long
 
const int N = 5e5 + 10;
int n, a[N], l[N], r[N];
LL pre[N], suf[N], b[N];

void solve() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        b[i] = a[i];
        l[i] = i - 1; r[i] = i + 1;
        pre[i] = pre[i - 1] + a[i];
    }
    for (int i = n; i >= 1; i--) {
        suf[i] = suf[i + 1] + a[i];
    }
    while (1) {
        bool flag = 0;
        for (int i = 1; i <= n; i++) {
            while (l[i] >= 1 && b[i] > a[l[i]]) {
                b[i] += pre[l[i]] - pre[l[l[i]]];
                l[i] = l[l[i]];
                flag = 1;
            }
        }
        for (int i = n; i >= 1; i--) {
            while (r[i] <= n && b[i] > a[r[i]]) {
                b[i] += suf[r[i]] - suf[r[r[i]]];
                r[i] = r[r[i]];
                flag = 1;
            }
        }
        if (!flag) break;
    }
    for (int i = 1; i <= n; i++) {
        cout << b[i] << ' ';
    }
}
 
int main() {
    // ios::sync_with_stdio(false);
    // cin.tie(nullptr);
    // cin >> t;
    solve();
    return 0;
}

笛卡尔树（特殊）

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define endl '\n'
#define LL long long
 
const int N = 5e5 + 10;
int n, a[N], ls[N], rs[N], k, stk[N];
LL ans[N], sum[N];
void dfs1(int x) {
    sum[x] = a[x];
    if (ls[x]) dfs1(ls[x]);
    if (rs[x]) dfs1(rs[x]);
    if (ls[x]) sum[x] += sum[ls[x]];
    if (rs[x]) sum[x] += sum[rs[x]];
}
void dfs(int x, int fa) {
    ans[x] = sum[x];
    if (fa && ans[x] > a[fa]) ans[x] = ans[fa];
    if (ls[x]) dfs(ls[x], x);
    if (rs[x]) dfs(rs[x], x);
}

void solve() {
    int top = 0;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        while(k > 0 && a[stk[k]] < a[i]) k--;
        if (k) rs[stk[k]] = i;
        if (k < top) ls[i] = stk[k + 1];
        stk[++k] = i;
        top = k;
    }
    dfs1(stk[1]);
    dfs(stk[1], 0);
    a[0] = a[n + 1] = 1e9 + 7;
    for (int i = 1; i <= n; i++) {
        if (a[i - 1] < a[i] || a[i] > a[i + 1]) cout << ans[i] << ' ';
        else cout << a[i] << ' ';
    }
}
 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    // cin >> t;
    solve();
    return 0;
}