problems: add unique paths

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

problems/unique-paths.cpp

@@ -0,0 +1,27 @@
+class Solution {
+    int right(const std::vector<int>& row, int size, int idx) const
+    {
+        if (idx >= size) {
+            return 0;
+        }
+        return row[idx];
+    }
+
+public:
+    int uniquePaths(int m, int n)
+    {
+        std::vector<int> bottom(n, 1);
+
+        for (int y = m - 2; y >= 0; y--) {
+            std::vector<int> above(n, 0);
+
+            for (int x = n - 1; x >= 0; x--) {
+                above[x] = right(above, n, x + 1) + bottom[x];
+            }
+
+            bottom = std::move(above);
+        }
+
+        return bottom[0];
+    }
+};