Hacktoberfest: add project euler for problem 206

DIRECTORY.md

@@ -712,6 +712,8 @@
     * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_174/sol1.py)
   * Problem 191
     * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_191/sol1.py)
+  * Problem 206
+    * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_206/sol1.py)
   * Problem 234
     * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_234/sol1.py)
   * Problem 551

project_euler/problem_206/sol1.py

@@ -0,0 +1,53 @@
+"""
+Problem 206 : https://projecteuler.net/problem=206
+
+Find the unique positive integer whose square has the form 1_2_3_4_5_6_7_8_9_0,
+where each “_” is a single digit.
+
+Solution: Finding a square number can found by adding consecutive odd numbers
+starting from 1. The minimum number possible for perfect square is 1020304050607080900
+in this situation, so started checking digits are in correct places after
+total is above it.
+"""
+
+import math
+
+
+def solution() -> int:
+    """
+    >>> solution()
+    1389019170
+    """
+
+    # adding odds
+    total = 1
+    add = 1
+
+    while True:
+
+        # adding odds
+        add += 2
+        total += add
+
+        # starts count here since the bottom limit
+        if total > 1020304050607080900:
+
+            # nested if statements to check digits
+            num = str(total)
+            if int(num[-1]) == 0:
+                if int(num[-3]) == 9:
+                    if int(num[-5]) == 8:
+                        if int(num[-7]) == 7:
+                            if int(num[-9]) == 6:
+                                if int(num[-11]) == 5:
+                                    if int(num[-13]) == 4:
+                                        if int(num[-15]) == 3:
+                                            if int(num[-17]) == 2:
+                                                if int(num[-19]) == 1:
+                                                    break
+
+    return int(math.sqrt(total))
+
+
+if __name__ == "__main__":
+    print(f"{solution() = }")