Create number-of-visible-people-in-a-queue.cpp

Author: kamyu104

C++/number-of-visible-people-in-a-queue.cpp

@@ -0,0 +1,39 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    vector<int> canSeePersonsCount(vector<int>& heights) {
+        vector<int> result(size(heights));
+        vector<int> stk;
+        for (int i = 0; i < size(heights); ++i) {
+            while (!empty(stk) && heights[stk.back()] <= heights[i]) {
+                ++result[stk.back()]; stk.pop_back();
+            }
+            if (!empty(stk)) {
+                ++result[stk.back()];
+            }
+            stk.emplace_back(i);
+        }
+        return result;
+    }
+};
+
+// Time:  O(n)
+// Space: O(n)
+class Solution2 {
+public:
+    vector<int> canSeePersonsCount(vector<int>& heights) {
+        vector<int> result(size(heights));
+        vector<int> stk;
+        for (int i = size(heights) - 1; i >= 0; --i) {
+            int cnt;
+            for (cnt = 0; !empty(stk) && heights[stk.back()] < heights[i]; ++cnt) {
+                stk.pop_back();
+            }
+            result[i] = !empty(stk) ? cnt + 1 : cnt;
+            stk.emplace_back(i);
+        }
+        return result;
+    }
+};