面试题64. 求1+2+…+n

Author: lzl124631x

leetcode-cn/面试题64. 求1+2+…+n/README.md

@@ -42,4 +42,20 @@ public:
                 + d(n, 7) + d(n, 8) + d(n, 9) + d(n, 10) + d(n, 11) + d(n, 12) + d(n, 13) + n) >> 1;
     }
 }
+```
+
+## Solution 2.
+
+```cpp
+// OJ: https://leetcode-cn.com/problems/qiu-12n-lcof/
+// Author: github.com/lzl124631x
+// Time: O(N)
+// Space: O(N)
+class Solution {
+public:
+    int sumNums(int n) {
+        n > 0 && (n += sumNums(n - 1));
+        return n;
+    }
+};
 ```