思路与算法

二分每个人最多抄写的页数B，范围为最大单本页数到全部页数和。顺序贪心把当前人尽量装满，所需人数≤k即B可行。求出最小B后，从最后一本倒着划分：给最后的人尽量多装，同时为前面每个人各留至少一本，再依次向前。输出每段书号。

正确性说明

固定B时，任何方案第一段的结束位置都不可能超过贪心结束位置；依次交换可知贪心所需人数最少。若少于k段，拆分非空段即可达到k段，故判定等价且单调。逆序重构在后面各段容量B内尽量吸收书，使前面剩余页数最少；若一个更早的划分能进一步减少最前未固定者的页数，则余下书本必须能由相同数量的后段容纳，与逆序最远吸收边界矛盾。逐段得到题目要求的前者尽量少抄的规范答案。

复杂度

设P为页数总和、D为P位数。含读入和重构，时间O(mD log P)，空间O(mD+k)；二分始终使用整数。

易错点

每本书不可拆，k个人各抄连续非空段且顺序不变；多解必须遵守前者少抄。页数无显式位数限制，标程使用大整数。

参考代码（C++11）

#include <bits/stdc++.h>
using namespace std;
struct cpp_int {
    string s;
    bool neg;
    cpp_int(long long v = 0) : s(to_string(v)), neg(v < 0) {
        if (neg)
            s.erase(s.begin());
    }
    void norm() {
        auto p = s.find_first_not_of('0');
        s = p == string::npos ? "0" : s.substr(p);
        if (s == "0")
            neg = false;
    }
    static int cmpabs(const cpp_int &a, const cpp_int &b) {
        if (a.s.size() != b.s.size())
            return a.s.size() < b.s.size() ? -1 : 1;
        return a.s == b.s ? 0 : a.s < b.s ? -1 : 1;
    }
    friend bool operator<(const cpp_int &a, const cpp_int &b) {
        if (a.neg != b.neg)
            return a.neg;
        int c = cmpabs(a, b);
        return a.neg ? c > 0 : c < 0;
    }
    friend bool operator==(const cpp_int &a, const cpp_int &b) {
        return a.neg == b.neg && a.s == b.s;
    }
    friend bool operator!=(const cpp_int &a, const cpp_int &b) {
        return !(a == b);
    }
    friend bool operator>(const cpp_int &a, const cpp_int &b) {
        return b < a;
    }
    friend bool operator<=(const cpp_int &a, const cpp_int &b) {
        return !(b < a);
    }
    friend bool operator>=(const cpp_int &a, const cpp_int &b) {
        return !(a < b);
    }
    cpp_int operator-() const {
        cpp_int r = *this;
        if (r.s != "0")
            r.neg = !r.neg;
        return r;
    }
    friend cpp_int operator+(const cpp_int &a, const cpp_int &b) {
        cpp_int r;
        r.s.clear();
        int carry = 0;
        if (a.neg == b.neg) {
            int i = (int)a.s.size() - 1, j = (int)b.s.size() - 1;
            while (i >= 0 || j >= 0 || carry) {
                int v = carry + (i >= 0 ? a.s[i--] - '0' : 0) + (j >= 0 ? b.s[j--] - '0' : 0);
                r.s += char('0' + v % 10);
                carry = v / 10;
            }
            r.neg = a.neg;
        } else {
            const cpp_int *x = &a, *y = &b;
            if (cmpabs(a, b) < 0)
                swap(x, y);
            int i = (int)x->s.size() - 1, j = (int)y->s.size() - 1;
            while (i >= 0) {
                int v = x->s[i--] - '0' - carry - (j >= 0 ? y->s[j--] - '0' : 0);
                carry = v < 0;
                if (carry)
                    v += 10;
                r.s += char('0' + v);
            }
            r.neg = x->neg;
        }
        reverse(r.s.begin(), r.s.end());
        r.norm();
        return r;
    }
    friend cpp_int operator-(const cpp_int &a, const cpp_int &b) {
        return a + (-b);
    }
    friend cpp_int operator*(const cpp_int &a, int b) {
        cpp_int r;
        r.s.clear();
        long long carry = 0;
        long long z = b;
        if (z < 0)
            z = -z;
        for (int i = (int)a.s.size() - 1; i >= 0; i--) {
            carry += (a.s[i] - '0') * z;
            r.s += char('0' + carry % 10);
            carry /= 10;
        }
        while (carry) {
            r.s += char('0' + carry % 10);
            carry /= 10;
        }
        reverse(r.s.begin(), r.s.end());
        r.neg = a.neg ^ (b < 0);
        r.norm();
        return r;
    }
    friend cpp_int operator/(const cpp_int &a, int b) {
        cpp_int r;
        r.s.clear();
        long long rem = 0, z = b;
        if (z < 0)
            z = -z;
        for (char c : a.s) {
            rem = rem * 10 + c - '0';
            r.s += char('0' + rem / z);
            rem %= z;
        }
        r.neg = a.neg ^ (b < 0);
        r.norm();
        return r;
    }
    cpp_int &operator+=(const cpp_int &b) {
        *this = *this + b;
        return *this;
    }
    cpp_int &operator-=(const cpp_int &b) {
        *this = *this - b;
        return *this;
    }
    cpp_int &operator*=(int b) {
        *this = *this * b;
        return *this;
    }
    friend istream &operator>>(istream &in, cpp_int &a) {
        string v;
        if (in >> v) {
            a.neg = v[0] == '-';
            if (v[0] == '-' || v[0] == '+')
                v.erase(v.begin());
            a.s = v;
            a.norm();
        }
        return in;
    }
    friend ostream &operator<<(ostream &out, const cpp_int &a) {
        if (a.neg)
            out << '-';
        return out << a.s;
    }
};

int main() {
    int m, k;
    cin >> m >> k;
    vector<cpp_int> a(m + 1);
    cpp_int lo = 0, hi = 0;
    for (int i = 1; i <= m; i++) {
        cin >> a[i];
        lo = max(lo, a[i]);
        hi += a[i];
    }
    auto possible = [&](const cpp_int &cap) {
        int used = 1;
        cpp_int sum = 0;
        for (int i = 1; i <= m; i++) {
            if (sum + a[i] > cap) {
                used++;
                sum = 0;
            }
            sum += a[i];
        }
        return used <= k;
    };
    while (lo < hi) {
        cpp_int mid = (lo + hi) / 2;
        if (possible(mid))
            hi = mid;
        else
            lo = mid + 1;
    }
    vector<pair<int, int>> out(k);
    int j = m;
    for (int person = k; person >= 1; person--) {
        int end = j;
        cpp_int sum = 0;
        while (j >= person && sum + a[j] <= lo) {
            sum += a[j];
            j--;
        }
        out[person - 1] = {j + 1, end};
    }
    for (auto p : out)
        cout << p.first << " " << p.second << "\n";
}