
Problem Statement
You are provided with two non-increasing integer arrays, nums1 and nums2, both using 0-based indexing. A valid pair of indices (i, j) is defined under two conditions: firstly, the index i from nums1 must not exceed the index j from nums2 (i <= j), and secondly, the value at nums1[i] must be less than or equal to the value at nums2[j] (nums1[i] <= nums2[j]). The distance of such a pair is the difference j - i. Your task is to determine the maximum possible distance for such valid index pairs and return this value. If no valid pairs exist, the function should return 0. Each array element must follow the non-increasing order, which means each subsequent element must be less than or equal to its predecessor.
Examples
Example 1
Input:
nums1 = [55,30,5,4,2], nums2 = [100,20,10,10,5]
Output:
2
Explanation:
The valid pairs are (0,0), (2,2), (2,3), (2,4), (3,3), (3,4), and (4,4). The maximum distance is 2 with pair (2,4).
Example 2
Input:
nums1 = [2,2,2], nums2 = [10,10,1]
Output:
1
Explanation:
The valid pairs are (0,0), (0,1), and (1,1). The maximum distance is 1 with pair (0,1).
Example 3
Input:
nums1 = [30,29,19,5], nums2 = [25,25,25,25,25]
Output:
2
Explanation:
The valid pairs are (2,2), (2,3), (2,4), (3,3), and (3,4). The maximum distance is 2 with pair (2,4).
Constraints
1 <= nums1.length, nums2.length <= 1051 <= nums1[i], nums2[j] <= 105- Both
nums1andnums2are non-increasing.
Approach and Intuition
Given the constraints and examples, the brute-force approach of comparing all possible pairs (i, j) with i from nums1 and j from nums2 is suboptimal due to potential high computational cost when array lengths are maximized. The following approach can be used for a more efficient solution:
Utilize a two-pointer technique to leverage the sorted (non-increasing) nature of
nums1andnums2.Set initial pointers at the start of both arrays. Begin with
i=0fornums1andj=0fornums2.Increase
juntilnums1[i]is less than or equal tonums2[j]orjreaches the end. This ensures compliance with the conditionnums1[i] <= nums2[j].If a valid
jis found fornums1[i], calculatej - iand update the maximum distance if this value exceeds the current known maximum.Move to the next element in
nums1by incrementingiand try to find a newjstarting from the currentj(sincenums2is non-increasing, a valid j fornums1[i]will be valid for all subsequenti).Repeat this until you have traversed all elements of
nums1while ensuring the above conditions.
- Return the recorded maximum distance. If no valid pairs were found (if the maximum distance wasn't updated), return 0.
This method works efficiently as each pointer only moves forward through its respective array, ensuring that every element is considered exactly once, achieving optimal performance in respect to time complexity.
Solutions
- C++
- Java
- Python
class Solution {
public:
int findMaxDistance(vector<int>& array1, vector<int>& array2) {
int maxDist = 0, index1 = 0, index2 = 0;
while (index1 < array1.size() && index2 < array2.size()) {
if (array1[index1] > array2[index2]) {
index1++;
} else {
maxDist = max(maxDist, index2 - index1);
index2++;
}
}
return maxDist;
}
};
This C++ solution addresses the problem of finding the maximum distance between a pair of values from two vectors where the value from the second vector is not smaller than the value from the first. The method findMaxDistance performs this check and determines the maximum permissible distance.
- The function initializes
maxDist,index1, andindex2to zero to keep track of the maximum distance and the current indices inarray1andarray2. - It employs a while loop to iterate through both arrays as long as neither index exceeds its respective array's length. This ensures all possible pairs of elements are considered.
- Inside the loop, a condition checks if the current element in
array1is greater than the element inarray2at their respective indices. If true, it incrementsindex1to check the next element inarray1. - If the element in
array1is not greater, it calculates the distance between the indices (index2 - index1) and updatesmaxDistif this new distance is greater than the previously recorded maximum distance. Subsequently,index2is incremented. - After the loop concludes,
maxDistholds the required maximum distance, which is then returned.
This approach ensures the solution is optimized and only viable pairs (where array1[index] is not greater than array2[index]) are considered, improving both clarity and efficiency of the algorithm.
class Solution {
public int maximumSeparation(int[] array1, int[] array2) {
int maxDiff = 0, index1 = 0, index2 = 0;
while (index1 < array1.length && index2 < array2.length) {
if (array1[index1] > array2[index2]) {
index1++;
} else {
maxDiff = Math.max(maxDiff, index2 - index1);
index2++;
}
}
return maxDiff;
}
}
This Java program aims to find the maximum distance between elements from two arrays under specific comparison conditions. The function maximumSeparation accepts two integer arrays, array1 and array2, and uses two pointers, index1 and index2, to traverse these arrays.
- Initialize
maxDiffto track the maximum separation distance. - Use a
whileloop to iterate through both arrays till one of them is fully traversed. - Compare elements from
array1andarray2:- If
array1[index1]is greater thanarray2[index2], incrementindex1. - Otherwise, calculate the difference between the current positions (
index2-index1) to updatemaxDiff, and incrementindex2.
- If
The function returns the value of maxDiff, which represents the largest valid index difference for which the value at array1[index1] is not greater than array2[index2]. This approach ensures an efficient O(n+m) complexity where n and m are the lengths of array1 and array2, respectively, by using a linear pass through the arrays without the need for nested loops.
class Solution:
def maximumGap(self, arr1: List[int], arr2: List[int]) -> int:
max_gap = 0
idx1, idx2 = 0, 0
while idx1 < len(arr1) and idx2 < len(arr2):
if arr1[idx1] > arr2[idx2]:
idx1 += 1
else:
max_gap = max(max_gap, idx2 - idx1)
idx2 += 1
return max_gap
The provided Python script defines a method to calculate the maximum gap in terms of indices between two sorted arrays, arr1 and arr2. The arrays must contain integers. The function, maximumGap, iterates through both arrays by using two pointers (idx1 for arr1 and idx2 for arr2) and computes the maximum gap where the value in arr1 is not greater than the value in arr2.
Follow these steps to understand the process implemented:
- Initialize
max_gapto 0, and pointer indicesidx1andidx2to 0. - Use a
whileloop to traverse elements in both arrays until one of the pointers reaches the end of its respective array. - Compare the current elements in
arr1andarr2using the pointers. - If the element in
arr1is greater, incrementidx1. - If the element in
arr1is less than or equal to the element inarr2, updatemax_gapif the current gap (idx2 - idx1) is larger than the recordedmax_gap, then incrementidx2. - Continue to loop until the end of one of the arrays.
- Return
max_gap, which is the maximum distance in indices between corresponding elements in the two arrays that meet the condition (arr1[idx1]<=arr2[idx2]).
This method is efficient with array traversal due to the use of two-pointer technique. Ensure that both arrays are sorted to properly utilize this method.