# Binary Search for Rational Numbers without using floating point arithmetic

A rational is represented as p/qb, for example 2/3. Given a sorted array of rational numbers, how to search an element using Binary Search. Use of floating point arithmetic is not allowed.

Example:

```Input:  arr[] = {1/5, 2/3, 3/2, 13/2}
x = 3/2
Output: Found at index 2
```

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To compare two rational numbers p/q and r/s, we can compare p*s with q*r.

 `// C program for Binary Search for Rationalnal Numbers ` `// without using floating point arithmetic ` `#include ` ` `  `struct` `Rational ` `{ ` `    ``int` `p; ` `    ``int` `q; ` `}; ` ` `  `// Utility function to compare two Rationalnal numbers ` `// 'a' and 'b'. It returns ` `// 0 --> When 'a' and 'b' are same ` `// 1 --> When 'a' is greater ` `//-1 --> When 'b' is greate ` `int` `compare(``struct` `Rational a, ``struct` `Rational b) ` `{ ` `    ``// If a/b == c/d  then  a*d = b*c: ` `    ``// method to ignore division ` `    ``if` `(a.p * b.q == a.q * b.p) ` `        ``return` `0; ` `    ``if` `(a.p * b.q > a.q * b.p) ` `        ``return` `1; ` `    ``return` `-1; ` `} ` ` `  `// Returns index of x in arr[l..r] if it is present, else ` `// returns -1. It mainly uses Binary Search. ` `int` `binarySearch(``struct` `Rational arr[], ``int` `l, ``int` `r, ` `                 ``struct` `Rational x) ` `{ ` `   ``if` `(r >= l) ` `   ``{ ` `        ``int` `mid = l + (r - l)/2; ` ` `  `        ``// If the element is present at the middle itself ` `        ``if` `(compare(arr[mid], x) == 0)  ``return` `mid; ` ` `  `        ``// If element is smaller than mid, then it can ` `        ``// only be present in left subarray ` `        ``if` `(compare(arr[mid], x) > 0) ` `            ``return` `binarySearch(arr, l, mid-1, x); ` ` `  `        ``// Else the element can only be present in right ` `        ``// subarray ` `        ``return` `binarySearch(arr, mid+1, r, x); ` `   ``} ` ` `  `   ``return` `-1; ` `} ` ` `  `// Driver method ` `int` `main() ` `{ ` `    ``struct` `Rational arr[] = {{1, 5}, {2, 3}, {3, 2}, {13, 2}}; ` `    ``struct` `Rational x = {3, 2}; ` `    ``int` `n = ``sizeof``(arr)/``sizeof``(arr); ` `    ``printf``(``"Element found at index %d"``, ` `            ``binarySearch(arr, 0, n-1, x)); ` `} `

Output:

`Element found at index 2`

Thanks to Utkarsh Trivedi for suggesting above solution.

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This article is attributed to GeeksforGeeks.org

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