2016. Maximum Difference Between Increasing Elements

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`

2016. Maximum Difference Between Increasing Elements
``````struct Solution;

impl Solution {
fn maximum_difference(nums: Vec<i32>) -> i32 {
let n = nums.len();
let mut res = -1;
for i in 0..n {
for j in i + 1..n {
if nums[i] < nums[j] {
res = res.max(nums[j] - nums[i]);
}
}
}
res
}
}

#[test]
fn test() {
let nums = vec![7, 1, 5, 4];
let res = 4;
assert_eq!(Solution::maximum_difference(nums), res);
let nums = vec![9, 4, 3, 2];
let res = -1;
assert_eq!(Solution::maximum_difference(nums), res);
let nums = vec![1, 5, 2, 10];
let res = 9;
assert_eq!(Solution::maximum_difference(nums), res);
}
``````