Formatted question description: https://leetcode.ca/all/2016.html

2016. Maximum Difference Between Increasing Elements (Easy)

Given a 0-indexed integer array nums of size n, find the maximum difference between nums[i] and nums[j] (i.e., nums[j] - nums[i]), such that 0 <= i < j < n and nums[i] < nums[j].

Return the maximum difference. If no such i and j exists, return -1.

 

Example 1:

Input: nums = [7,1,5,4]
Output: 4
Explanation:
The maximum difference occurs with i = 1 and j = 2, nums[j] - nums[i] = 5 - 1 = 4.
Note that with i = 1 and j = 0, the difference nums[j] - nums[i] = 7 - 1 = 6, but i > j, so it is not valid.

Example 2:

Input: nums = [9,4,3,2]
Output: -1
Explanation:
There is no i and j such that i < j and nums[i] < nums[j].

Example 3:

Input: nums = [1,5,2,10]
Output: 9
Explanation:
The maximum difference occurs with i = 0 and j = 3, nums[j] - nums[i] = 10 - 1 = 9.

 

Constraints:

  • n == nums.length
  • 2 <= n <= 1000
  • 1 <= nums[i] <= 109

Similar Questions:

Solution 1. Brute force

// OJ: https://leetcode.com/problems/maximum-difference-between-increasing-elements/
// Time: O(N^2)
// Space: O(1)
class Solution {
public:
    int maximumDifference(vector<int>& A) {
        int N = A.size(), ans = -1;
        for (int i = 0; i < N; ++i) {
            for (int j = i + 1; j < N; ++j) {
                if (A[i] < A[j]) ans = max(ans, A[j] - A[i]);
            }
        }
        return ans;
    }
};

Solution 2. DP

// OJ: https://leetcode.com/problems/maximum-difference-between-increasing-elements/
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int maximumDifference(vector<int>& A) {
        int N = A.size(), ans = -1, mn = INT_MAX;
        for (int i = 0; i < N; ++i) {
            mn = min(mn, A[i]);
            if (A[i] > mn) ans = max(ans, A[i] - mn);
        }
        return ans;
    }
};

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