Create largest-plus-sign.cpp

C++/largest-plus-sign.cpp

@@ -0,0 +1,48 @@
+// Time:  O(n^2)
+// Space: O(n^2)
+
+class Solution {
+public:
+    int orderOfLargestPlusSign(int N, vector<vector<int>>& mines) {
+        unordered_set<pair<int, int>, PairHash<int>> lookup;
+        for (const auto& mine : mines) {
+            lookup.emplace(mine[0], mine[1]);
+        }
+        vector<vector<int>> dp(N, vector<int>(N));
+        int result = 0;
+        for (int i = 0; i < N; ++i) {
+            for (int j = 0, l = 0; j < N; ++j) {
+                l = lookup.count(make_pair(i, j)) ? 0 : l + 1;
+                dp[i][j] = l;
+            }
+            for (int j = N - 1, l = 0; j >= 0; --j) {
+                l = lookup.count(make_pair(i, j)) ? 0 : l + 1;
+                dp[i][j] = min(dp[i][j], l);
+            }
+        }
+
+        for (int j = 0; j < N; ++j) {
+            for (int i = 0, l = 0; i < N; ++i) {
+                l = lookup.count(make_pair(i, j)) ? 0 : l + 1;
+                dp[i][j] = min(dp[i][j], l);
+            }
+            for (int i = N - 1, l = 0; i >= 0; --i) {
+                l = lookup.count(make_pair(i, j)) ? 0 : l + 1;
+                dp[i][j] = min(dp[i][j], l);
+                result = max(result, dp[i][j]);
+            }
+        }
+        return result;
+    }
+
+private:
+    template <typename T>
+    struct PairHash {
+        size_t operator()(const pair<T, T>& p) const {
+            size_t seed = 0;
+            seed ^= std::hash<T>{}(p.first)  + 0x9e3779b9 + (seed<<6) + (seed>>2);
+            seed ^= std::hash<T>{}(p.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
+            return seed;
+        }
+    };
+};