PROBLEM DESCRIPTION
Given two arrays of integers a[] and b[] of size n and m, the task is to check if a pair of values (one value from each array) exists such that swapping the elements of the pair will make the sum of two arrays equal.
Note: Return 1 if there exists any such pair otherwise return -1.
SOLUTION
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class Solution {
long findSwapValues(long a[], int n, long b[], int m) {
long sum1 = getSum(a);
long sum2 = getSum(b);
long diff = sum1 - sum2;
// let's say we are looking for x in arr1 and y in arr2
// what we need is:
// sum1 - x + y = sum2 - y + x
// => sum1 - sum2 = 2 * (x - y)
// => diff = 2 * (x - y)
// if diff is odd, no pair will be possible
if(diff%2 != 0)
return -1;
// store all numbers in 2nd array in a hashset for quick lookup
Set<Long> set = new HashSet<>();
for(int i=0; i<m; i++)
set.add(b[i]);
// iterate over the first array
for(int i=0; i<n; i++){
// assume current num to x
long x = a[i];
// diff = 2x - 2y
// 2y = 2x - diff
// y = (2x - diff)/2
// we can determine value of y based on x and diff
long y = x - diff/2;
// if y is present in second array, return 1
if(set.contains(y))
return 1;
}
return -1;
}
long getSum(long[] arr){
long sum = 0;
for(int i=0; i<arr.length; i++)
sum += arr[i];
return sum;
}
}