AtCoder Beginner Contest 124

A - Buttons

#include <bits/stdc++.h>

using namespace std;

int main() {
	int a, b;
	cin >> a >> b;
	int res = 0;
	if(a > b) res += a, a --;
	else res += b, b --;

	if(a > b) res += a, a --;
	else res += b, b --;
	cout << res << "\n";	
	return 0;
}

B - Great Ocean View

#include <bits/stdc++.h>

using namespace std;

using vi = vector<int>;

int main() {
	int n;
	cin >> n;
	vi h(n);
	for(auto &i : h) cin >> i;
	int res = 1, pre = h[0];
	for(int i = 1; i < n; i ++){
		res += (h[i] >= pre);
		pre = max(pre, h[i]);
	}
	cout << res << "\n";
	return 0;
}

C - Coloring Colorfully

动态规划

#include <bits/stdc++.h>

using namespace std;

using vi = vector<int>;

int main() {
	string s;
	cin >> s;
	int n = s.size();
	s = " " + s;
	vector<array<int,2>> f(n + 1);
	for(int i = 1, x; i <= n ; i ++) {
		x = s[i] - '0';
		f[i][x] = f[i-1][x ^ 1];
		f[i][x ^ 1] = f[i-1][x] + 1;
	}
	cout << min(f[n][0], f[n][1]);
	return 0;
}

D - Handstand

双指针

#include <bits/stdc++.h>

using namespace std;

using vi = vector<int>;

int main() {
    ios::sync_with_stdio(false), cin.tie(nullptr);
    int n, k;
    cin >> n >> k;

    string s;
    cin >> s;
    s += '.';

    vector<int> a, b;
    for (int i = 1, cnt = 1; i < s.size(); i++) {
        if (s[i] == s[i - 1]) cnt++;
        else {
            a.push_back(cnt);
            b.push_back(s[i - 1] - '0');
            cnt = 1;
        }
    }
    int m = a.size();
    int res = 0;
    for (int l = 0, r = -1, cnt = 0, len = 0; l < m; l++) {
        while (r + 1 < m and cnt + (b[r + 1] == 0) <= k)
            r++, cnt += (b[r] == 0), len += a[r];
        res = max(res, len);
        cnt -= (b[l] == 0), len -= a[l];
    }
    cout << res << "\n";
    return 0;
}