# Closest greater element for every array element from another array

Given two arrays a[] and b[], we need to build an array c[] such that every element c[i] of c[] contains a value from a[] which is greater than b[i] and is closest to b[i]. If a[] has no greater element than b[i], then value of c[i] is -1. All arrays are of same size.

Examples:

```Input : a[] = [ 2, 6, 5, 7, 0]
b[] = [1, 3, 2, 5, 8]
Output : c[] = [2, 5, 5, 7, -1]

Input : a[] = [ 2, 6, 5, 7, 0]
b[] = [0, 2, 3, 5, 1]
Output : c[] = [2, 5, 5, 6, 2]
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Naive Approach : For each element in b[], we traverse the whole of a[] and try to find the closest greater element, and save the result for each search. This will cost time complexity of O(n^2).

Efficient Approach : Sort the array a[], and for each b[i], apply binary search in sorted array a[]. For this method our time complexity will be O(nlogn).
Note: For closest greater element we can use upper_bound().

Below is the implementation.

## C++

 `// CPP to find result from target array ` `// for closest element ` `#include ` `using` `namespace` `std; ` ` `  `// Function for printing resultant array ` `void` `closestResult(``int` `a[], ``int` `b[], ``int` `n) ` `{ ` `    ``// change arr[] to vector ` `    ``vector<``int``> vect(a, a + n); ` ` `  `    ``// sort vector for ease ` `    ``sort(vect.begin(), vect.end()); ` ` `  `    ``// iterator for upper_bound ` `    ``vector<``int``>::iterator up; ` ` `  `    ``// vector for result ` `    ``vector<``int``> c; ` ` `  `    ``// calculate resultant array ` `    ``for` `(``int` `i = 0; i < n; i++) { ` ` `  `        ``// check upper bound element ` `        ``up = upper_bound(vect.begin(), vect.end(), b[i]); ` ` `  `        ``// if no element found push -1 ` `        ``if` `(up == vect.end()) ` `            ``c.push_back(-1); ` ` `  `        ``// Else push the element ` `        ``else` `            ``c.push_back(*up); ``// add to resultant ` `    ``} ` ` `  `    ``cout << ``"Result = "``; ` `    ``for` `(``auto` `it = c.begin(); it != c.end(); it++) ` `        ``cout << *it << ``" "``; ` `} ` ` `  `// driver program ` `int` `main() ` `{ ` `    ``int` `a[] = { 2, 5, 6, 1, 8, 9 }; ` `    ``int` `b[] = { 2, 1, 0, 5, 4, 9 }; ` `    ``int` `n = ``sizeof``(a) / ``sizeof``(a); ` `    ``closestResult(a, b, n); ` `    ``return` `0; ` `} `

## Java

 `// Java to find result from target array  ` `// for closest element ` `import` `java.util.*; ` ` `  `class` `GFG  ` `{ ` ` `  `    ``// Function for printing resultant array ` `    ``static` `void` `closestResult(Integer[] a,  ` `                              ``int``[] b, ``int` `n)  ` `    ``{ ` ` `  `        ``// change arr[] to Set ` `        ``TreeSet vect = ``new` `TreeSet<>(Arrays.asList(a)); ` ` `  `        ``// vector for result ` `        ``Vector c = ``new` `Vector<>(); ` ` `  `        ``// calculate resultant array ` `        ``for` `(``int` `i = ``0``; i < n; i++)  ` `        ``{ ` ` `  `            ``// check upper bound element ` `            ``Integer up = vect.higher(b[i]); ` ` `  `            ``// if no element found push -1 ` `            ``if` `(up == ``null``) ` `                ``c.add(-``1``); ` ` `  `            ``// Else push the element ` `            ``else` `                ``c.add(up); ``// add to resultant ` `        ``} ` ` `  `        ``System.out.print(``"Result = "``); ` `        ``for` `(``int` `i : c) ` `            ``System.out.print(i + ``" "``); ` `    ``} ` ` `  `    ``// Driver Code ` `    ``public` `static` `void` `main(String[] args)  ` `    ``{ ` `        ``Integer[] a = { ``2``, ``5``, ``6``, ``1``, ``8``, ``9` `}; ` `        ``int``[] b = { ``2``, ``1``, ``0``, ``5``, ``4``, ``9` `}; ` `        ``int` `n = a.length; ` ` `  `        ``closestResult(a, b, n); ` `    ``} ` `} ` ` `  `// This code is contributed by ` `// sanjeev2552 `

## Python3

 `# Python implementation to find result ` `# from target array for closest element ` ` `  `import` `bisect ` ` `  `# Function for printing resultant array ` `def` `closestResult(a, b, n): ` `     `  `    ``# sort list for ease ` `    ``a.sort() ` ` `  `    ``# list for result ` `    ``c ``=` `[] ` ` `  `    ``# calculate resultant array ` `    ``for` `i ``in` `range``(n): ` ` `  `        ``# check location of upper bound element ` `        ``up ``=` `bisect.bisect_right(a, b[i]) ` ` `  `        ``# if no element found push -1 ` `        ``if` `up ``=``=` `n: ` `            ``c.append(``-``1``) ` `         `  `        ``# else puch the element ` `        ``else``: ` `            ``c.append(a[up]) ``# add to resultant ` `     `  `    ``print``(``"Result = "``, end ``=` `"") ` `    ``for` `i ``in` `c: ` `        ``print``(i, end ``=` `" "``) ` ` `  ` `  `# Driver code ` `if` `__name__ ``=``=` `"__main__"``: ` `    ``a ``=` `[``2``,``5``,``6``,``1``,``8``,``9``] ` `    ``b ``=` `[``2``,``1``,``0``,``5``,``4``,``9``] ` `    ``n ``=` `len``(a) ` `    ``closestResult(a, b, n) ` ` `  `# This code is contributed by ` `# sanjeev2552 `

Output:

```Result = 5 2 1 6 5 -1
```

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