Codeforces 1141F2（贪心、预处理）

要点

• 一开始dp然后码力太辣鸡并且算法带假于是调了很久一交还WA在28……
• 吐槽完毕。后来想拿栈优化dp时发现其实完全不需要dp，贪心选取即可，当前的不兼容就干脆不要它了，结果不会变差。然后想要什么就预处理什么即可。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <unordered_map>
using namespace std;

const int maxn = 1505;
int n, a[maxn], sum[maxn], ans, val, ID;
int d[maxn * maxn], cnt;
vector<int> v[maxn * maxn];
vector<int> vv[maxn];
unordered_map<int, int> mp, L[maxn];

int main() {   
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
        scanf("%d", &a[i]), sum[i] = sum[i - 1] + a[i];
    for (int i = 1; i <= n; i++) {
        for (int j = i - 1; ~j; j--) {
            int t = sum[i] - sum[j];
            d[++cnt] = t;
            if (!L[i][t])   L[i][t] = j + 1, vv[i].push_back(t);
        }
    }

    sort(d + 1, d + 1 + cnt);
    cnt = unique(d + 1, d + 1 + cnt) - d - 1;
    for (int i = 1; i <= cnt; i++)  mp[d[i]] = i; 
        
    for (int i = 1; i <= n; i++) {
        for (int j = 0; j < vv[i].size(); j++) {
            int t = vv[i][j], id = mp[t];
            if (v[id].empty() || v[id].back() < L[i][t]) {
                v[id].push_back(i);
            }
            if (ans < v[id].size()) {
                ans = v[id].size();
                val = t;
                ID = id;
            }
        }
    }

    printf("%d
", ans);
    for (int i : v[ID]) {
        printf("%d %d
", L[i][val], i);
    }
    return 0;
}