...

Makefile

@@ -1,4 +1,4 @@
-CXXFLAGS=-Wall -Wextra -std=c++11
+CXXFLAGS=-Wall -Wextra -std=c++11 -g
 SHELL=bash
 
 .PHONY: run

g.cpp

@@ -0,0 +1,60 @@
+#include <iostream>
+#include <queue>
+#include <tuple>
+
+using namespace std;
+
+using pos   = tuple<long, long>;
+using node  = tuple<long, long>;
+
+const auto MAX = static_cast<long>(1e10);
+
+int main()
+{
+  long m, n, x; cin >> m >> n;
+  vector<vector<node>> vault(m, vector<node>(n));
+  vector<vector<bool>> seen(m, vector<bool>(n, false));
+  for (long i = 0; i < m; ++i) {
+    for (long j = 0; j < n; ++j) {
+      cin >> x; vault[i][j] = make_tuple(x, MAX);
+    }
+  }
+  auto neighbors = [m,n](pos p) {
+    long i = get<0>(p), j = get<1>(p);
+    vector<pos> ns; ns.reserve(4);
+    if (i >   0) ns.push_back(make_tuple(i-1,j));
+    if (i < m-1) ns.push_back(make_tuple(i+1,j));
+    if (j >   0) ns.push_back(make_tuple(i,j-1));
+    if (j < n-1) ns.push_back(make_tuple(i,j+1));
+    return ns;
+  };
+  auto length = [&vault](pos a, pos b) {
+    auto d = get<0>(vault[get<0>(b)][get<1>(b)]) - get<0>(vault[get<0>(a)][get<1>(a)]);
+    return d <= 0 ? 0 : d;
+  };
+  priority_queue<tuple<long, pos>> q;
+  q.push(make_tuple(0, make_tuple(0, 0))); get<1>(vault[0][0]) = 0;
+  while (!q.empty()) {
+    auto u    = get<1>(q.top()); q.pop();
+    long i    = get<0>(u), j = get<1>(u);
+    auto & vu = vault[i][j];
+    // cerr << "(" << get<0>(u) << "," << get<1>(u) << ") " << endl;
+    if (seen[i][j]) continue;
+    for (auto & v : neighbors(u)) {
+      auto & vv = vault[get<0>(v)][get<1>(v)];
+      auto d    = max(get<1>(vu), length(u, v));
+      // cerr << "(" << get<0>(v) << "," << get<1>(v) << ") " << get<1>(vv) << " " << d << endl;
+      if (d < get<1>(vv)) {
+        get<1>(vv) = d; q.push(make_tuple(-d, v));
+      }
+    }
+    seen[i][j] = true;
+  }
+  //  for (long i = 0; i < m; ++i) {
+  //    for (long j = 0; j < n; ++j) {
+  //      cerr << get<1>(vault[i][j]) << " ";
+  //    }
+  //    cerr << endl;
+  //  }
+  cout << get<1>(vault[m-1][n-1]) << endl;
+}