Added find all indices of occurrences of a value

snippets/indices_of_occurence.md

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+---
+title: indices_of_occurrence
+tags: list,beginner
+---
+
+Returns a list of indices of all the occurrences of an element in a list.
+
+- Use `enumerate()` to get index and value simultaneously while iterating.
+- Use `==` to check equality, if current element `val` is equal to `value`. Then `idx` to list.
+
+```py
+def indices_of_occurrence(lst, value):
+  return [idx for idx, val in enumerate(lst) if val == value]
+```
+
+```py
+indices_of_occurrence([1, 2, 1, 4, 5, 1], 1) # [0, 2, 5]
+indices_of_occurrence([1, 2, 3, 4], 6) # [] 
+```