From http://blog.csdn.net/qq_33765907/article/details/51228610

ZOJ/3942_csdn.cpp

@@ -0,0 +1,121 @@
+#include <bits/stdc++.h>
+using namespace std;
+typedef long long LL;
+typedef pair<int, int> PII;
+typedef vector<int> VI;
+typedef vector<PII> VP;
+
+class Solution {
+  static const int MAXN = 2000 + 10;
+  int a[MAXN], n, m;
+  LL count00(LL ret = 0) {
+    map<VI, VP> mp;
+    for (int i = 1; i < n; i += 2) {
+      VI pt; int sum = 0;
+      for (int j = i; j + 1 < n; ++j) {
+        pt.push_back(a[j]);
+        if (j & 1) {
+          if (a[i - 1] + sum + a[j + 1] >= m) {
+            mp[pt].push_back(PII(a[i - 1], a[j + 1]));
+          }
+        } else sum += a[j];
+        if (sum >= m) break;
+      }
+    }
+    for (auto &e: mp) {
+      VP &y = e.second, x;
+      int sum = m;
+      for (size_t i = 1; i < e.first.size(); i += 2) sum -= e.first[i];
+      for (auto &v: y) {
+        int L = v.first, R = v.second;
+        v.first = max(1, sum - R);
+        v.second = min(L, sum - 1);
+        if (v.first <= v.second) x.push_back(v);
+      }
+      if (x.empty()) continue;
+      sort(x.begin(), x.end());
+      int l = x[0].first, r = x[0].second;
+      for (size_t i = 0; i < x.size(); ++i) {
+        if (x[i].first <= r) r = max(r, x[i].second);
+        else {
+          ret += r - l + 1;
+          l = x[i].first;
+          r = x[i].second;
+        }
+      }
+      ret += r - l + 1;
+    }
+    return ret;
+  }
+  LL count10(LL ret = 0) {
+    map<VI, int> mp;
+    for (int i = 1; i < n; i += 2) {
+      VI pt; int sum = 0;
+      for (int j = i + 1; j < n; ++j) {
+        pt.push_back(a[j]);
+        if (~j & 1) {
+          sum += a[j];
+          if (sum >= m) {
+            sum -= a[j];
+            pt.pop_back();
+            pt.push_back(m - sum);
+            mp[pt] = max(mp[pt], a[i]);
+            break;
+          }
+        }
+      }
+    }
+    for (auto &e: mp) ret += e.second;
+    return ret;
+  }
+  LL count11(LL ret = 0) {
+    map<VI, VP> mp;
+    for (int i = 2; i < n; i += 2) {
+      VI pt; int sum = 0;
+      for (int j = i; j + 1 < n; ++j) {
+        pt.push_back(a[j]);
+        if (~j & 1) {
+          sum += a[j];
+          if (sum == m) mp[pt].push_back(PII(a[i - 1], a[j + 1]));
+          else if (sum > m) break;
+        }
+      }
+    }
+    for (auto &e: mp) {
+      VP &y = e.second;
+      sort(y.begin(), y.end());
+      for (int i = y.size() - 2; i >= 0; --i) {
+        y[i].second = max(y[i].second, y[i + 1].second);
+      }
+      for (size_t i = 0; i < y.size(); ++i) {
+        int extra = i ? y[i].first - y[i - 1].first : y[i].first;
+        ret += 1ll * extra * y[i].second;
+      }
+    }
+    return ret;
+  }
+public:
+  void run() {
+    scanf("%d%d", &n, &m);
+    for (int i = 0; i < n; ++i) scanf("%d", a + i);
+    LL ret = count00() + count11();
+    ret += count10();
+    if (n % 2 == 0) a[n++] = 0;
+    reverse(a, a + n);
+    ret += count10();
+    for (int i = 0; i < n; i += 2) if (a[i] >= m && m) {
+      ++ret; break;
+    }
+    if (m == 0) {
+      ret = 0;
+      for (int i = 1; i < n; i += 2) ret = max(ret, (LL)a[i]);
+    }
+    printf("%lld\n", ret);
+  }
+} sol;
+
+int main() {
+  int T; scanf("%d", &T);
+  for (int cas = 1; cas <= T; ++cas) sol.run();
+  return 0;
+}