#1858. 【LOJ2392】「JOISC 2017 Day 1」烟花棒

https://sjzezoj.com/submission/68611

S2OJ/1858/1858.cpp

@@ -0,0 +1,115 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, k, t;
+long long x[N], a[N];
+
+bool check(int v) {
+    for (int i = 1; i <= n; i++) {
+        a[i] = x[i] - 2ll * v * t * i;
+    }
+
+    if (a[n] > a[1]) {
+        return false;
+    }
+
+    int l = k, r = k;
+
+    for (int i = k - 1; i >= 1; i--) {
+        if (a[l] - a[i] <= 0) l = i;
+    }
+
+    for (int i = k + 1; i <= n; i++) {
+        if (a[i] - a[r] <= 0) r = i;
+    }
+
+    int l1 = k, r1 = k;
+
+    while (l < l1 || r1 < r) {
+        int nl = l1, nr = r1;
+        bool flag = false;
+
+        while (l < nl && a[r1] - a[nl - 1] <= 0) {
+            if (a[l1] - a[--nl] <= 0) break;
+        }
+
+        if (nl < l1 && a[l1] - a[nl] <= 0) {
+            l1 = nl;
+            flag = true;
+        }
+
+        while (nr < r && a[nr + 1] - a[l1] <= 0) {
+            if (a[++nr] - a[r1] <= 0) break;
+        }
+
+        if (r1 < nr && a[nr] - a[r1] <= 0) {
+            r1 = nr;
+            flag = true;
+        }
+
+        if (!flag) return false;
+    }
+
+    int l2 = 1, r2 = n;
+
+    while (l2 < l || r < r2) {
+        int nl = l2, nr = r2;
+        bool flag = false;
+
+        while (nl < l && a[r2] - a[nl + 1] <= 0) {
+            if (a[++nl] - a[l2] >= 0) break;
+        }
+
+        if (l2 < nl && a[nl] - a[l2] >= 0) {
+            l2 = nl;
+            flag = true;
+        }
+
+        while (r < nr && a[nr - 1] - a[l2] <= 0) {
+            if (a[r2] - a[--nr] >= 0) break;
+        }
+
+        if (nr < r2 && a[r2] - a[nr] >= 0) {
+            r2 = nr;
+            flag = true;
+        }
+
+        if (!flag) return false;
+    }
+
+    return true;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n >> k >> t;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> x[i];
+    }
+
+    int l = 0, r = 1e9,
+        res = 0;
+
+    while (l <= r) {
+        int mid = (l + r) >> 1;
+
+        if (check(mid)) {
+            r = mid - 1;
+            res = mid;
+        } else {
+            l = mid + 1;
+        }
+    }
+
+    cout << res << endl;
+
+    return 0;
+}