Maximize value of (arr[i] – i) – (arr[j] – j) in an array

MaximizeArrayDiff.js

// Maximize value of (arr[i] – i) – (arr[j] – j) in an array

// Given an array, arr[] find the maximum value of (arr[i] – i) – (arr[j] – j) where i is not equal to j. 
// Where i and j vary from 0 to n-1 and n is size of input array arr[].

// Examples:

// Input : arr[] = {9, 15, 4, 12, 13}
// Output : 12
// We get the maximum value for i = 1 and j = 2
// (15 - 1) - (4 - 2) = 12

// Input : arr[] = {-1, -2, -3, 4, 10}
// Output : 6
// We get the maximum value for i = 4 and j = 2
// (10 - 4) - (-3 - 2) = 11


///Analysis
// pre-compute will help reduce the runtime but increase the Space requirement to O(2N) but that's still acceptable as space will still be O(N) 
/// and time will also be O(N)
// My solution
// (1) I ll precompute arr[i] - i for all elements and save it in another array B
// (2) I ll find min(B) and max(B) 
// (3) difference of max(B) and min(B) will be the maximum value
// steps 1,2,3 all are of the order O(N) timewise, therefore the algorithm is O(N) overall

function findDiffArray(inputArray) {
	diffArray = [];
	for(i=0;i<inputArray.length;i++) {
		diffArray[i] = inputArray[i] -i;
	}
	return diffArray;
}

function minValInArray(inputArray) {
	var min=Number.MAX_VALUE;
	for(i=0;i<inputArray.length;i++) {
		if (min > inputArray[i]) 
			min = inputArray[i];
	}
	return min;
}

function maxValInArray(inputArray) {
	var max=Number.MIN_VALUE;
	for(i=0;i<inputArray.length;i++) {
		if (max < inputArray[i]) 
			max = inputArray[i];
	}
	return max;
}

function solution(inputArray) {
	da = findDiffArray(inputArray);
	minv=minValInArray(da);
	maxv=maxValInArray(da);
	return maxv - minv;
}

/////////////////////////
///verification
/////////////////////////
console.log(solution([9, 15, 4, 12, 13]));
console.log(solution([-1, -2, -3, 4, 10]));