problems: add pascals triangle

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/pascals-triangle.cpp

@@ -0,0 +1,30 @@
+class Solution {
+    int getN(const vector<int>& previousRow, int n)
+    {
+        if (n == 0 || n == previousRow.size()) {
+            return 1;
+        }
+        return previousRow[n - 1] + previousRow[n];
+    }
+
+public:
+    vector<vector<int>> generate(int numRows)
+    {
+        if (numRows <= 0) {
+            return {};
+        }
+
+        vector<vector<int>> result { vector<int> { 1 } };
+        for (auto i = 2; i <= numRows; i++) {
+            auto& previous = result.back();
+            vector<int> current;
+
+            for (auto j = 0; j < i; j++) {
+                current.push_back(getN(previous, j));
+            }
+            result.push_back(move(current));
+        }
+
+        return result;
+    }
+};