Submission #845968

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Source Code Expand

#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

int main() {
	long long int n;
	cin >> n;
	vector<long long int> a(n, 0);
	for (long long int i = 0; i < n; i++) {
		cin >> a[i];
	}
	long long int c = 0;
	vector<long long int> b(n, 0);
	for (long long int i = 0; i < n; i++) {
		if (a[i] % 2 == 0 && a[i] >= 2) {
			c += (a[i]-2)/2;
			a[i] = 2;
		} else if (a[i] % 2 == 1) {
			c += a[i]/2;
			a[i] = 1;
		}
		b[i] = a[i];
	}
	long long int aa = 0;
	long long int bb = 0;
	for (long long int i = 0; i < n-1; i++) {
		if (a[i] == 2) {
			a[i] = 0;
			aa++;
		} else if (a[i] == 1 && a[i+1] >= 1) {
			aa++;
			a[i] = 0;
			a[i+1]--;
		}
	}
	if (a[n-1] == 2) {
		aa++;
	}
	for (long long int i = n-1; i > 0; i--) {
		if (b[i] == 2) {
			b[i] = 0;
			bb++;
		} else if (b[i] == 1 && b[i-1] >= 1) {
			bb++;
			b[i] = 0;
			b[i-1]--;
		}
	}
	if (b[0] == 2) {
		bb++;
	}
	cout << c+max(aa, bb) << endl;
	return 0;
}

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