ps：改了这么久，对拍一下就找到错误了。贪心，首部出现的1，是不用去剪的，所以当作特殊元素考虑，因此当 k == 0的时候 或者 k没有用完的时候一定要考虑是否用到了首部那一节（cntSt)。而尾部只需要剪一次，中间的部分需要减两次，贪心的时候要分别讨论（有史以来写得最丑的代码！！！)

inline bool cmp(P a, P b) {    return a.first > b.first;}int main(){    while (scanf("%d %d", &n, &k) != EOF) {        scanf("%s", s);        int cntSt = 0, cntEd = 0, st = 0, ed = n - 1;        for (int i = 0; i < n; ++i) {            if (s[i] != '1') {                st = i;                break;            }            else cntSt++;        }        for (int i = n - 1; ~i; --i) {            if (s[i] != '1') {                ed = i;                break;            }            else cntEd++;        }        if (cntEd == n) {            cout << n << endl;            continue;        }        vector
     
       ans;        ans.clear();        mem(use, 0);        P p[N];        int t = 0;        for (int i = st; i <= ed; ++i) {            if (s[i] == '1') t++;            else {                if (t) ans.pb(t);                t = 0;            }        }        if (t) ans.pb(t);        if (k == 0) {            cout << cntSt << endl;            continue;        }        if (k == 1) {            int res = cntEd + cntSt;            for (int i = 0; i < ans.size(); ++i) upd(res, ans[i]);            cout << res << endl;            continue;        }        for (int i = 0; i < ans.size(); ++i) p[i].first = ans[i], p[i].second = 0;        if (cntEd) p[ans.size()].first = cntEd, p[ans.size()].second = 1;        sort(p, p + ans.size() + 1, cmp);        int res = 0;        for (int i = 0; i < ans.size() + 1; ++i) {            if (!k) break;            if (p[i].second == 1) {                res += p[i].first;                k--;                use[cntEd] = 1;                if (k == 0) res += cntSt;            }            else {                if (k > 2) {                    res += p[i].first;                    k -= 2;                }                else if (k == 2) {                    if (use[cntEd]) res += p[i].first + cntSt;                    else res += max(p[i].first + cntSt, p[i].first + cntEd);                    k -= 2;                }                else if (k == 1) {                    if (use[cntEd]) res += max(cntSt, p[i].first);                    else res += max(cntSt + cntEd, p[i].first);                    k--;                }            }        }        if (k) res += cntSt;        cout << res << endl;    }    return 0;}