Codeforces 442c Artem and array (stack + greedy)

Connection: codeforces 442c Artem and array

The following figure shows an array. Each time a number is deleted, the score for deleting a number is the minimum value of the number on both sides. If either of the two sides does not exist, the score is 0. Ask the maximum score.

Solution: first, remove the continuous A, B, C, A> B & C> B and get min (a, B) points, in this way, the array is converted into a sequence with a descending order. Except for the largest and second largest numbers, other numbers can be scored.

Example: 4 10 2 2 8

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;typedef long long ll;const int N = 5 * 1e5 + 5;int n, c = -1;ll stack[N];int main () {    ll x, ans = 0;    scanf("%d", &n);    for (int i = 0; i < n; i++) {        scanf("%lld", &x);        while (c > 0 && stack[c-1] >= stack[c] && stack[c] < x) {            ans += min(stack[c-1], x);            c--;        }        stack[++c] = x;    }    sort (stack, stack + c + 1);    for (int i = 0; i <= c - 2; i++)        ans += stack[i];    printf("%lld\n", ans);    return 0;}