message: Update contains-duplicate-iii.cpp
diff: @@ -18,7 +18,7 @@ public:
  bst.erase(bst.find(num));
  }
  // Every search costs time: O(logk).
  - const auto it = bst.lower_bound(nums[i] - t);
  + const auto it = bst.lower_bound(static_cast<int64_t>(nums[i]) - t);
  if (it == bst.cend() || (*it - nums[i]) > t) {
  // Not found.
  window.emplace(nums[i]);
  