diff --git a/climbing-stairs/s0ooo0k.java b/climbing-stairs/s0ooo0k.java
new file mode 100644
index 000000000..9ebe00120
--- /dev/null
+++ b/climbing-stairs/s0ooo0k.java
@@ -0,0 +1,17 @@
+class Solution {
+    /*
+     * 시간복잡도 O(n)
+     * 공간복잡도 O(n)
+    */
+    public int climbStairs(int n) {
+        int[] piv = new int[n+1];
+        piv[0]=1;
+        piv[1]=2;
+
+        for(int i=2; i<n; i++) {
+            piv[i]=piv[i-1]+piv[i-2];
+        }
+        return piv[n-1];
+    }
+}
+
diff --git a/valid-anagram/s0ooo0k.java b/valid-anagram/s0ooo0k.java
new file mode 100644
index 000000000..56989afdc
--- /dev/null
+++ b/valid-anagram/s0ooo0k.java
@@ -0,0 +1,23 @@
+class Solution {
+    /*
+     * 초반 풀이시 단순 s의 문자가 t에 포함하는지만 확인하여 제대로된 비교를 못함 (ex "sass" vs "saas")
+     * 따라서 정렬 후 비교하는 방식으로 전환
+     * 
+     * 시간복잡도 O(n log n)
+     * 공간복잡도 O(n)
+     */
+    public boolean isAnagram(String s, String t) {
+    
+        if(s.length() != t.length()) 
+            return false;        
+        
+        char[] chr1 = s.toCharArray();
+        char[] chr2 = t.toCharArray();
+
+        Arrays.sort(chr1);
+        Arrays.sort(chr2);
+
+        return Arrays.equals(chr1, chr2);
+    }
+}
+
diff --git a/validate-binary-search-tree/s0ooo0k.java b/validate-binary-search-tree/s0ooo0k.java
new file mode 100644
index 000000000..a8e48786a
--- /dev/null
+++ b/validate-binary-search-tree/s0ooo0k.java
@@ -0,0 +1,15 @@
+/*
+ * 시간복잡도 : O(n)
+ */
+
+class Solution {
+    public boolean isValidBST(TreeNode root) {
+        return valid(root, Long.MIN_VALUE, Long.MAX_VALUE);
+    }
+    private boolean valid(TreeNode node, long min, long max) {
+        if(node==null) return true;
+        if(node.val <= min || node.val >=max) return false;
+        return valid(node.left, min, node.val) && valid(node.right, node.val, max);
+    }
+}
+