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Given an array ** ‘ARR’** of

Find and return the number which occurs an odd number of times.

```
'N' = 5, 'ARR' = [1, 2, 3, 2, 3]
Output: 1
Except for number 1, all numbers occur an even number of times.
```

Detailed explanation

```
9
4 5 6 5 6 9 9 4 4
```

```
4
```

```
5, 6, and 9 occur an even number of times, and only 4 occur odd number of times.
```

```
5
1 1 1 1 1
```

```
1
```

```
1 <= 'N' <= 10^5
1 <= 'ARR[i]' <= 10^5
Time Limit: 1 sec
```