diff --git a/Problems/src/Bit/word_square.py b/Problems/src/Bit/word_square.py
new file mode 100644
index 0000000..cb0cd45
--- /dev/null
+++ b/Problems/src/Bit/word_square.py
@@ -0,0 +1,60 @@
+"""
+Word Square definition, 0<=k<n(width/length), row k and column k are idenitcal
+eg: row 1: ABCD and column 1:ABCD are the same
+"""
+from copy import deepcopy
+
+
+def word_square(strs, k):
+    """
+    :type strs: List[str], k: int
+    :rtype: List[List[str]]
+    """
+    strs_filtered = [s for s in strs if len(s) <= k]
+    path, res = [], []
+    for i, string in enumerate(strs_filtered):
+        if len(string) == k:
+            path.append(string)
+            strs_filtered.remove(string)
+            dfs(strs_filtered, k, path, 1, res)
+            strs_filtered.insert(i, string)
+            path.pop()
+    return res
+
+
+def validate(step, path, string):
+    """
+    :type ....
+    :rtype: boolean
+    """
+    for i in range(min(len(string), len(path))):
+        if len(path[i]) <= step or string[i] != path[i][step]:
+            return False
+    return True
+
+
+def dfs(strs, k, path, step, res):
+    """
+    :type tickets: List[List[str]]
+    :rtype: List[str]
+    """
+    if step == k:
+        res.append(deepcopy(path))
+        return
+    min_length = 0
+    while min_length < len(path):
+        if len(path[min_length]) < step:
+            break
+        min_length += 1
+    strs_filtered = [s for s in strs if len(s) >= min_length]
+    for i, string in enumerate(strs_filtered):
+        if validate(step, path, string):
+            path.append(string)
+            strs.remove(string)
+            dfs(strs, k, path, step + 1, res)
+            strs.insert(i, string)
+            path.pop()
+
+
+TEST = ["ABCD", "BNRT", "CRMY", "DTYE", "CRM", "DT", "DTY"]
+print word_square(TEST, 4)