Create the-number-of-weak-characters-in-the-game.cpp

Author: kamyu104

C++/the-number-of-weak-characters-in-the-game.cpp

@@ -0,0 +1,50 @@
+// Time:  O(nlogn)
+// Space: O(1)
+
+class Solution {
+public:
+    int numberOfWeakCharacters(vector<vector<int>>& properties) {
+        sort(begin(properties), end(properties),
+             [](const auto& a, const auto& b) {
+                 return a[0] == b[0] ? a[1] > b[1] : a[0] < b[0];
+             });
+        int result = 0, max_d = 0;
+        for (int i = size(properties) - 1; i >= 0; --i) {
+            if (properties[i][1] < max_d) {
+                ++result;
+            }
+            max_d = max(max_d, properties[i][1]);
+        }
+        return result;
+    }
+};
+
+// Time:  O(nlogn)
+// Space: O(n)
+// faster in sort by using more space
+class Solution2 {
+public:
+    int numberOfWeakCharacters(vector<vector<int>>& properties) {
+        unordered_map<int, vector<int>> lookup;
+        for (const auto& p : properties) {
+            lookup[p[0]].emplace_back(p[1]);
+        }
+        vector<int> sorted_as;
+        for (const auto& [a, _] : lookup) {
+            sorted_as.emplace_back(a);
+        }
+        sort(begin(sorted_as), end(sorted_as), greater<int>());
+        int result = 0, max_d = 0;
+        for (const auto& a : sorted_as) {
+            for (const auto& d : lookup[a]) {
+                if (d < max_d) {
+                    ++result;
+                }
+            }
+            for (const auto& d : lookup[a]) {
+                max_d = max(max_d, d);
+            }
+        }
+        return result;
+    }
+};