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Queries to find the minimum index in given array having at least value X
• Difficulty Level : Medium
• Last Updated : 24 Feb, 2021

Given an array arr[] of size N and an array Q[] consisting of M integers, each representing a query, the task for each query Q[i] is to find the smallest index of an array element whose value is greater than or equal to Q[i]. If no such index exists, then print -1.

Examples:

Input: arr[] = { 1, 9 }, Q[] = { 7, 10, 0 }
Output: 1 -1 0
Explanation:
The smallest index of arr[] whose value is greater than Q[0] is 1.
No such index exists in arr[] whose value is greater than Q[1].
The smallest index of arr[] whose value is greater than Q[2] is 0.
Therefore, the required output is 1 -1 0.

Input: arr[] = {2, 3, 4}, Q[] = {2, 3, 4}
Output: 0 1 2

Approach:The problem can be solved using Binary search and Prefix Sum technque. Follow the steps below to solve the problem:

Below is the implementation of the above approach:

## C++

 `// C++ program to implement``// the above approach``#include ``using` `namespace` `std;` `// Function to find the smallest index``// of an array element whose value is``// less than or equal to Q[i]``void` `minimumIndex(vector<``int``>& arr,``                  ``vector<``int``>& Q)``{` `    ``// Stores size of array``    ``int` `N = arr.size();` `    ``// Stores coun of queries``    ``int` `M = Q.size();` `    ``// Store array elements along``    ``// with the index``    ``vector > storeArrIdx;` `    ``// Store smallest index of an array``    ``// element whose value is greater``    ``// than or equal to i``    ``vector<``int``> minIdx(N);` `    ``// Traverse the array``    ``for` `(``int` `i = 0; i < N; ++i) {` `        ``// Insert {arr[i], i} into``        ``// storeArrIdx[]``        ``storeArrIdx.push_back({ arr[i], i });``    ``}` `    ``// Sort the array``    ``sort(arr.begin(), arr.end());` `    ``// Sort the storeArrIdx``    ``sort(storeArrIdx.begin(),``         ``storeArrIdx.end());` `    ``// Stores index of arr[N - 1] in``    ``// sorted order``    ``minIdx[N - 1]``        ``= storeArrIdx[N - 1].second;` `    ``// Traverse the array storeArrIdx[]``    ``for` `(``int` `i = N - 2; i >= 0; i--) {` `        ``// Update minIdx[i]``        ``minIdx[i] = min(minIdx[i + 1],``                        ``storeArrIdx[i].second);``    ``}` `    ``// Traverse the array Q[]``    ``for` `(``int` `i = 0; i < M; i++) {` `        ``// Store the index of``        ``// lower_bound of Q[i]``        ``int` `pos``            ``= lower_bound(arr.begin(),``                          ``arr.end(), Q[i])``              ``- arr.begin();` `        ``// If no index found whose value``        ``// greater than or equal to arr[i]``        ``if` `(pos == N) {``            ``cout << -1 << ``" "``;``            ``continue``;``        ``}` `        ``// Print smallest index whose value``        ``// greater than or equal to Q[i]``        ``cout << minIdx[pos] << ``" "``;``    ``}``}` `// Driver Code``int` `main()``{` `    ``vector<``int``> arr = { 1, 9 };``    ``vector<``int``> Q = { 7, 10, 0 };` `    ``minimumIndex(arr, Q);``    ``return` `0;``}`

## Java

 `// Java program for above approach``import` `java.util.*;``import` `java.lang.*;``class` `pair``{``  ``int` `element,index;``  ``pair(``int` `element, ``int` `index)``  ``{``    ``this``.element = element;``    ``this``.index = index;``  ``}``}``class` `GFG``{` `  ``// Function to find the smallest index``  ``// of an array element whose value is``  ``// less than or equal to Q[i]``  ``static` `void` `minimumIndex(``int``[] arr,``                           ``int``[] Q)``  ``{` `    ``// Stores size of array``    ``int` `N = arr.length;` `    ``// Stores coun of queries``    ``int` `M = Q.length;` `    ``// Store array elements along``    ``// with the index``    ``ArrayList storeArrIdx = ``new` `ArrayList<>();` `    ``// Store smallest index of an array``    ``// element whose value is greater``    ``// than or equal to i``    ``int``[] minIdx = ``new` `int``[N];` `    ``// Traverse the array``    ``for` `(``int` `i = ``0``; i < N; ++i)``    ``{` `      ``// Insert {arr[i], i} into``      ``// storeArrIdx[]``      ``storeArrIdx.add(``new` `pair(arr[i], i));``    ``}` `    ``// Sort the array``    ``Arrays.sort(arr);` `    ``// Sort the storeArrIdx``    ``Collections.sort(storeArrIdx, (a, b)->a.element-b.element);` `    ``// Stores index of arr[N - 1] in``    ``// sorted order``    ``minIdx[N - ``1``]``      ``= storeArrIdx.get(N - ``1``).index;` `    ``// Traverse the array storeArrIdx[]``    ``for` `(``int` `i = N - ``2``; i >= ``0``; i--) {` `      ``// Update minIdx[i]``      ``minIdx[i] =Math.min(minIdx[i + ``1``],``                          ``storeArrIdx.get(i).index);``    ``}` `    ``// Traverse the array Q[]``    ``for` `(``int` `i = ``0``; i < M; i++) {` `      ``// Store the index of``      ``// lower_bound of Q[i]``      ``int` `pos``        ``= lower_bound(arr, Q[i]);` `      ``// If no index found whose value``      ``// greater than or equal to arr[i]``      ``if` `(pos == N) {``        ``System.out.print(``"-1"``+``" "``);``        ``continue``;``      ``}` `      ``// Print smallest index whose value``      ``// greater than or equal to Q[i]``      ``System.out.print(minIdx[pos]+``" "``);``    ``}``  ``}``  ``static` `int` `lower_bound(``int``[] arr,``int` `element)``  ``{``    ``for``(``int` `i = ``0``; i < arr.length; i++)``      ``if``(element <= arr[i])``        ``return` `i;` `    ``return` `arr.length; ``  ``}` `  ``// Driver function``  ``public` `static` `void` `main (String[] args)``  ``{``    ``int``[] arr = { ``1``, ``9` `};``    ``int``[] Q = { ``7``, ``10``, ``0` `};` `    ``minimumIndex(arr, Q);``  ``}``}` `// This code is contributed by offbeat`

## Python3

 `# Python3 program to implement``# the above approachf``from` `bisect ``import` `bisect_left` `# Function to find the smallest index``# of an array element whose value is``# less than or equal to Q[i]``def` `minimumIndex(arr, Q):` `    ``# Stores size of array``    ``N ``=` `len``(arr)` `    ``# Stores coun of queries``    ``M ``=` `len``(Q)` `    ``# Store array elements along``    ``# with the index``    ``storeArrIdx ``=` `[]` `    ``# Store smallest index of an array``    ``# element whose value is greater``    ``# than or equal to i``    ``minIdx ``=` `[``0``]``*``(N)` `    ``# Traverse the array``    ``for` `i ``in` `range``(N):``      ` `        ``# Insert {arr[i], i} into``        ``# storeArrIdx[]``        ``storeArrIdx.append([arr[i], i])` `    ``# Sort the array``    ``arr ``=` `sorted``(arr)` `    ``# Sort the storeArrIdx``    ``storeArrIdx ``=` `sorted``(storeArrIdx)` `    ``# Stores index of arr[N - 1] in``    ``# sorted order``    ``minIdx[N ``-` `1``] ``=` `storeArrIdx[N ``-` `1``][``1``]` `    ``# Traverse the array storeArrIdx[]``    ``for` `i ``in` `range``(N ``-` `2``, ``-``1``, ``-``1``):` `        ``# Update minIdx[i]``        ``minIdx[i] ``=` `min``(minIdx[i ``+` `1``], storeArrIdx[i][``1``])` `    ``# Traverse the array Q[]``    ``for` `i ``in` `range``(M):` `        ``# Store the index of``        ``# lower_bound of Q[i]``        ``pos ``=` `bisect_left(arr, Q[i])` `        ``# If no index found whose value``        ``# greater than or equal to arr[i]``        ``if` `(pos ``=``=` `N):``            ``print``(``-``1``, end ``=` `" "``)``            ``continue` `        ``# Prsmallest index whose value``        ``# greater than or equal to Q[i]``        ``print``(minIdx[pos], end ``=` `" "``)` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ``arr ``=` `[``1``, ``9``]``    ``Q ``=` `[``7``, ``10``, ``0``]``    ``minimumIndex(arr, Q)` `    ``# This code is contributed by mohit kumar 29`
Output:
`1 -1 0`

Time Complexity: O(N * log(N))
Auxiliary Space: O(N)

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