Update index.md

Replace solutions with challenges

Author: subsr97

index.md

@@ -1,9 +1,9 @@
 # Daily Coding Problem
-1. [Sum Pair in Array](./solutions/sum-pair-in-array.py)
-2. [Product Array Puzzle](./solutions/product-array-puzzle.py)
-3. [Serialize and Deserialize Binary Tree](./solutions/serialize-and-deserialize-binary-tree.py)
-4. [First Missing Positive](./solutions/first-missing-positive.py)
-5. [Function Implementation](./solutions/function-implementation.py)
-6. [XOR Linked List](./solutions/xor-linked-list.py)
-7. [Decode Ways](./solutions/decode-ways.py)
-8. [Count Unival Subtrees](./solutions/count-unival-subtrees.py)
+1. [Sum Pair in Array](./challenges/sum-pair-in-array.py)
+2. [Product Array Puzzle](./challenges/product-array-puzzle.py)
+3. [Serialize and Deserialize Binary Tree](./challenges/serialize-and-deserialize-binary-tree.py)
+4. [First Missing Positive](./challenges/first-missing-positive.py)
+5. [Function Implementation](./challenges/function-implementation.py)
+6. [XOR Linked List](./challenges/xor-linked-list.py)
+7. [Decode Ways](./challenges/decode-ways.py)
+8. [Count Unival Subtrees](./challenges/count-unival-subtrees.py)