题解 | #DNA序列#

// 利用滑动窗口的解法，效率更高
#include<iostream>
#include<string>
using namespace std;

int main() {
    string s;
    int n;
    while (cin >> s >> n) {
        int len = s.length();
        int resindex = 0, max = 0;
        int count = 0;
        for (int i = 0; i < n; i++) //录入最前面的窗口
            if (s[i] == 'C' || s[i] == 'G')
                count++;

        max = count; //录下第一个窗口的CG数量作为最大
        int left = 1, right = n; //从录入窗口的左右点右移一位开始
        while (right < len) { //直到右窗口结束
            if (s[left - 1] == 'C' || s[left - 1] == 'G') //窗口左边出去的是CG
                count--;
            if (s[right] == 'C' || s[right] == 'G') //窗口右边进来的是CG
                count++;
            if (count > max) { //更新，取最大值
                max = count;
                resindex = left;
            }
            left++;
            right++;
        }
        cout << s.substr(resindex, n) << endl; //根据下标和n输出
    }
    return 0;
}