Codeforces Round 378 Div2 Problem C

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CF733C Epidemic in Monstropolis

Solution Sketch

Key observations:

  1. Use prefix table to group initial weights of the monsters to match weights of the monsters after the joke. (make sure to check if grouping is possible or not -> WA test case 119)
  2. For each group, if the maximum number in that group has a smaller number on its left or right, then reduction is possible.

AC Code

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#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<int, int> ii;
vector<pair<int, char>> ans;
bool check(vector<int> num, int offset)
{
    // printf("%d\n", offset);
    /*
       for(int i = 0; i < (int)num.size(); i++) {
       printf("%d: %d\n", i, num[i]);
       }
     */
    if ((int)num.size() == 1)
        return true;
    int mx = 0;
    for (int i = 0; i < (int)num.size(); i++)
        mx = max(mx, num[i]);
    for (int i = 0; i < (int)num.size(); i++) {
        if (num[i] == mx) {
            if (i - 1 >= 0 && num[i - 1] < mx) {
                int l = i;
                l = l < 0 ? 0 : l;
                int r = (int)num.size() - 1 - i;
                r = r < 0 ? 0 : r;
                // printf("%d %d\n", l, r);
                int pos = i;
                for (int j = 0; j < l; j++) {
                    // printf("%d L\n", offset + pos--);
                    ans.push_back(make_pair(offset + pos--, 'L'));
                }
                for (int j = 0; j < r; j++) {
                    // printf("%d R\n", offset);
                    ans.push_back(make_pair(offset, 'R'));
                }
                return true;
            } else if (i + 1 < (int)num.size() && num[i + 1] < mx) {
                int l = i;
                l = l < 0 ? 0 : l;
                int r = (int)num.size() - 1 - i;
                r = r < 0 ? 0 : r;
                // printf("%d %d\n", l, r);
                int pos = i;
                for (int j = 0; j < r; j++) {
                    // printf("%d R\n", offset);
                    ans.push_back(make_pair(offset + i, 'R'));
                }
                for (int j = 0; j < l; j++) {
                    // printf("%d L\n", offset + pos--);
                    ans.push_back(make_pair(offset + pos--, 'L'));
                }
                return true;
            }
        }
    }
    return false;
}
int main()
{
    int n;
    scanf("%d", &n);
    int inp[n + 1];
    for (int i = 1; i <= n; i++)
        scanf("%d", &inp[i]);
    int prefix[n + 1];
    prefix[0] = 0;
    for (int i = 1; i <= n; i++)
        prefix[i] = prefix[i - 1] + inp[i];
    int m;
    scanf("%d", &m);
    int end[m + 1];
    for (int i = 1; i <= m; i++)
        scanf("%d", &end[i]);
    vector<int> num;
    int prev = 0, idx = 1;
    bool error = false;
    for (int i = 1; i <= n + 1; i++) {
        // printf("%d %d\n", i, prev);
        if (prefix[i] - prefix[prev] <= end[idx] && i != n + 1) {
            num.push_back(inp[i]);
        } else {
            if (prefix[i - 1] - prefix[prev] != end[idx]) {
                error = true;
                break;
            }
            if (check(num, idx) == false) {
                error = true;
                break;
            }
            prev = i - 1;
            num.clear();
            idx++;
            num.push_back(inp[i]);
        }
    }
    if (idx - 1 == m && error == false) {
        printf("YES\n");
        for (auto i : ans)
            printf("%d %c\n", i.first, i.second);
    } else {
        printf("NO\n");
    }
    return 0;
}