Added solution for find the number of ways to place people i.

C++/find-the-number-of-ways-to-place-people-i.cpp

@@ -0,0 +1,58 @@
+// Time:  O(n^2)
+// Space: O(1)
+
+// sort, array
+class Solution {
+public:
+    int numberOfPairs(vector<vector<int>>& points) {
+        sort(begin(points), end(points), [](const auto& a, const auto& b) {
+            return a[0] != b[0] ? a[0] < b[0] : a[1] > b[1];
+        });
+
+        int result = 0;
+        for (int i = 0; i < size(points); ++i) {
+            for (int j = i + 1, y = numeric_limits<int>::min(); j < size(points); ++j) {
+                if (points[i][1] < points[j][1]) {
+                    continue;
+                }
+                if (points[j][1] > y) {
+                    y = points[j][1];
+                    ++result;
+                }
+            }
+        }
+        return result;
+    }
+};
+
+// Time:  O(n^3)
+// Space: O(1)
+// sort, array
+class Solution2 {
+public:
+    int numberOfPairs(vector<vector<int>>& points) {
+        sort(begin(points), end(points), [](const auto& a, const auto& b) {
+            return a[0] != b[0] ? a[0] < b[0] : a[1] > b[1];
+        });
+
+        int result = 0;
+        for (int i = 0; i < size(points); ++i) {
+            for (int j = i + 1, y = numeric_limits<int>::min(); j < size(points); ++j) {
+                if (points[i][1] < points[j][1]) {
+                    continue;
+                }
+                bool valid = true;
+                for (int k = i + 1; k < j; ++k) {
+                    if (points[i][1] >= points[k][1] && points[k][1] >= points[j][1]) {
+                        valid = false;
+                        break;
+                    }
+                }
+                if (valid) {
+                    ++result;
+                }
+            }
+        }
+        return result;
+    }
+};