Codeforces Round #555 (Div. 3) C2 - Increasing Subsequence (hard version) 贪心模拟

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类似于C1，从两边先选小的，

如果一样大的话，那接下来选的只能是某一边连续的一段，

这样的话分别从两边开始选，最后看哪个结果最优

注意判断是否合法

#include <bits/stdc++.h>
#include <iostream>
using namespace std;
typedef long long ll;

const int maxn = 2e5 + 7;

int n;
int a[maxn];

int solve1(int l, int r, int x) {
    if(a[l] <= x) return 0;
    int res = 1;
    int t = l+1;
    while(t < r) {
        if(a[t] > a[t-1]) res++;
        else break;
        t++;
    }
    return res;
}

int solve2(int l, int r, int x) {
    if(a[r] <= x) return 0;
    int res = 1;
    int t = r-1;
    while(t > l) {
        if(a[t] > a[t+1]) res++;
        else break;
        t--;
    }
    return res;
}

int main() {
    scanf("%d", &n);
    for(int i = 1; i <= n; ++i) {
        scanf("%d", &a[i]);
    }
    int l = 1, r = n;
    vector<char> ans;
    int t = 0;
    while(l <= r) {
        if(l == r) {
            if(a[l] > t) ans.push_back('L');
            break;
        }
        if(a[l] < a[r]) {
            if(a[l] > t) {
                ans.push_back('L');
                t = a[l];
                l++;
            }
            else if(a[r] > t){
                ans.push_back('R');
                t = a[r];
                r--;
            }
            else break;
        }
        else if(a[l] > a[r]) {
            if(a[r] > t) {
                ans.push_back('R');
                t = a[r];
                r--;
            }
            else if(a[l] > t){
                ans.push_back('L');
                t = a[l];
                l++;
            }
            else break;
        }
        else if(a[l] == a[r]) {
            int t1 = solve1(l, r, t);
            int t2 = solve2(l, r, t);
            if(t1 >= t2) {
                for(int j = 0; j < t1; ++j) {
                    ans.push_back('L');
                }
                break;
            }
            else {
                for(int j = 0; j < t2; ++j) {
                    ans.push_back('R');
                }
                break;
            }
        }
    }
    cout << ans.size() << endl;
    for(auto i : ans) {
        printf("%c", i);
    }
    return 0;
}