#1812. 【2017.3 长乐省选集训 Day10 T2】划分序列

https://sjzezoj.com/submission/66456

S2OJ/1812/1812.cpp

@@ -0,0 +1,127 @@
+#include <iostream>
+#include <algorithm>
+#include <functional>
+#include <iterator>
+#include <numeric>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 5e4 + 5;
+const int INF = 0x3f3f3f3f;
+
+template <typename T>
+struct Max {
+    T operator()(T a, T b) const {
+        return std::max(a, b);
+    }
+};
+
+template <typename T>
+struct Min {
+    T operator()(T a, T b) const {
+        return std::min(a, b);
+    }
+};
+
+template <typename T, int N, class Operator = std::plus<int>>
+class BIT {
+  private:
+    T default_val;
+    T c[N];
+
+    unsigned lowbit(unsigned x) {
+        return x & -x;
+    }
+
+  public:
+    BIT(const T& init_val = 0)
+        : default_val(init_val) {
+        std::fill(std::begin(c), std::end(c), init_val);
+    }
+
+    void add(unsigned x, T v) {
+        for (; x < N; x += lowbit(x)) {
+            c[x] = Operator()(c[x], v);
+        }
+    }
+
+    T query(T x) {
+        T res = default_val;
+
+        for (; x; x -= lowbit(x)) {
+            res = Operator()(res, c[x]);
+        }
+
+        return res;
+    }
+};
+
+int n, k, a[N], s[N];
+
+bool check(int x) {
+    int res_min = 0,
+        res_max = 0;
+    std::vector<int> nums;
+    BIT<int, N << 1, Max<int>> bit_max(-INF);
+    BIT<int, N << 1, Min<int>> bit_min(INF);
+
+    std::copy(s + 1, s + 1 + n, std::back_inserter(nums));
+    std::transform(nums.begin(), nums.end(), nums.begin(), std::bind(std::minus<int>(), std::placeholders::_1, x));
+    std::copy(s, s + n, std::back_inserter(nums));
+    std::sort(nums.begin(), nums.end());
+    nums.erase(std::unique(nums.begin(), nums.end()), nums.end());
+
+    int pos = nums.size() - (std::lower_bound(nums.begin(), nums.end(), 0) - nums.begin() + 1) + 1;
+
+    bit_min.add(pos, 0);
+    bit_max.add(pos, 0);
+
+    for (int i = 1; i <= n; i++) {
+        pos = nums.size() - (std::lower_bound(nums.begin(), nums.end(), s[i] - x) - nums.begin() + 1) + 1;
+        res_min = bit_min.query(pos);
+        res_max = bit_max.query(pos);
+
+        if (i < n) {
+            pos = nums.size() - (std::lower_bound(nums.begin(), nums.end(), s[i]) - nums.begin() + 1) + 1;
+            bit_min.add(pos, res_min + 1);
+            bit_max.add(pos, res_max + 1);
+        }
+    }
+
+    return ++res_min <= k && k <= ++res_max;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> k;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    std::partial_sum(a + 1, a + 1 + n, s + 1);
+
+    int l = -INF,
+        r = INF,
+        ans = 0;
+
+    while (l <= r) {
+        int mid = (l + r) >> 1;
+
+        if (check(mid)) {
+            ans = mid;
+            r = mid - 1;
+        } else {
+            l = mid + 1;
+        }
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}