Description
You are given an integer array nums of length n and an integer k.
For each index i, define its instability score as max(nums[0..i]) - min(nums[i..n - 1]).
In other words:
max(nums[0..i])is the largest value among the elements from index 0 to indexi.min(nums[i..n - 1])is the smallest value among the elements from indexito indexn - 1.
An index i is called stable if its instability score is less than or equal to k.
Return the smallest stable index. If no such index exists, return -1.
Example 1:
Input: nums = [5,0,1,4], k = 3
Output: 3
Explanation:
- At index 0: The maximum in
[5]is 5, and the minimum in[5, 0, 1, 4]is 0, so the instability score is5 - 0 = 5. - At index 1: The maximum in
[5, 0]is 5, and the minimum in[0, 1, 4]is 0, so the instability score is5 - 0 = 5. - At index 2: The maximum in
[5, 0, 1]is 5, and the minimum in[1, 4]is 1, so the instability score is5 - 1 = 4. - At index 3: The maximum in
[5, 0, 1, 4]is 5, and the minimum in[4]is 4, so the instability score is5 - 4 = 1. - This is the first index with an instability score less than or equal to
k = 3. Thus, the answer is 3.
Example 2:
Input: nums = [3,2,1], k = 1
Output: -1
Explanation:
- At index 0, the instability score is
3 - 1 = 2. - At index 1, the instability score is
3 - 1 = 2. - At index 2, the instability score is
3 - 1 = 2. - None of these values is less than or equal to
k = 1, so the answer is -1.
Example 3:
Input: nums = [0], k = 0
Output: 0
Explanation:
At index 0, the instability score is 0 - 0 = 0, which is less than or equal to k = 0. Therefore, the answer is 0.
Constraints:
1 <= nums.length <= 1000 <= nums[i] <= 1090 <= k <= 109
Solutions
Corrected and simplified.
Language: javascript(2026-09-04 07:25)DONE
CPU Performance96.30%
Memory Performance48.15%
/**
* @param {number[]} nums
* @param {number} k
* @return {number}
*/
var firstStableIndex = function(nums, k) {
const n = nums.length;
const prefixSum = Array(n);
prefixSum[0] = nums[0];
const suffixSum = Array(n);
suffixSum[n - 1] = nums[n - 1];
for (let i = 1; i < n; i++) {
prefixSum[i] = Math.max(prefixSum[i - 1], nums[i]);
const j = n - 1 - i;
suffixSum[j] = Math.min(suffixSum[j + 1], nums[j]);
}
for (let i = 0; i < n; i++) {
if (prefixSum[i] - suffixSum[i] <= k) {
return i;
}
}
return -1;
};