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# Python | Find common elements in three sorted arrays by intersecting a dictionary

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Examples:

` Input: ar1 = [1, 5, 10, 20, 40, 80] ar2 = [6, 7, 20, 80, 100] ar3 = [3, 4, 15 , 20, 30, 70, 80, 120] Output: [80, 20] Input: ar1 = [1, 5, 5] ar2 = [3, 4, 5, 5, 10] ar3 = [5, 5, 10 , 20] Output: [5, 5] `

We have a solution to this problem, please refer to the link Find common elements in three sorted arrays . We can quickly fix this problem in python using intersection dictionaries. The approach is simple,

1. First convert all three lists to dictionaries with elements as keys and their frequencies as values ​​using the Counter () .
2. Now perform intersection operation for three dictionaries, as a result we get a dictionary that has common elements among three lists of arrays with their frequencies.

 ` # Function to find common elements in three ` ` # sorted arrays ` ` from ` ` collections ` ` import ` ` Counter ` ` `  ` def ` ` commonElement (ar1, ar2, ar3): ` ` # convert lists to dictionary first ` ` ` ` ar1 ` ` = ` ` Counter (ar1) ` ` ar2 ` ` = ` ` Counter (ar2) ` ` ` ` ar3 ` ` = ` ` Counter (ar3) `   ` # perform the operation intersections ` ` resultDict ` ` = ` ` dict ` ` (ar1.items () & amp; ar2.items () & amp; ar3.items ()) ` ` common ` ` = ` ` [] `   ` # iterate over the resulting dictionary ` ` # and collect shared elements ` ` for ` ` (key, val) ` ` in ` ` resultDict.items (): ` ` for ` ` i ` ` in ` ` range ` ` (` ` 0 ` ` , val): ` ` common.append (key) ` ` `  ` ` ` print ` ` ( common) `   ` # Driver program ` ` if ` ` __ name__ ` ` = ` ` = ` ` "__ main__" ` `: ` ` ar1 ` ` = ` ` [` ` 1 ` `, ` ` 5 ` `, ` ` 10 ` `, ` ` 20 ` `, ` ` 40 ` `, ` ` 80 ` `] ` ` ar2 ` ` = ` ` [` ` 6 ` `, ` ` 7 ` `, ` ` 20 ` `, ` ` 80 ` `, ` ` 100 ` `] ` ` ar3 ` ` = ` ` [` ` 3 ` `, ` ` 4 ` `, ` ` 15 ` `, ` ` 20 ` `, ` ` 30 ` `, ` ` 70 ` `, ` ` 80 ` `, ` ` 120 ` `] `  ` commonElement (ar1, ar2, ar3) `

Exit:

` [80, 20] `

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