LeetCode 2420: Find All Good Indices Solution

Master LeetCode problem 2420 (Find All Good Indices), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2420. Find All Good Indices

Medium

Array Dynamic Programming Prefix Sum

Problem Explanation

Explanation

To solve this problem, we iterate through the array and check each index satisfying the given conditions. We can use two pointers to traverse the k elements before and after the current index, ensuring they are in non-increasing and non-decreasing order respectively. If both conditions are met, we add the index to the result array.

Start by initializing an empty list to store the good indices.
Iterate through the array from index k to n-k.
For each index i, check the k elements before and after i to ensure they are in the required order.
If both conditions are satisfied, add i to the result list.
Finally, return the list of good indices sorted in increasing order.

The time complexity of this solution is O(n) as we iterate through the entire array once. The space complexity is O(1) as we are not using any additional space proportional to the input size.

Solution Code

class Solution {
    public List<Integer> findGoodIndices(int[] nums, int k) {
        List<Integer> goodIndices = new ArrayList<>();
        for (int i = k; i < nums.length - k; i++) {
            if (checkGoodIndex(nums, i, k)) {
                goodIndices.add(i);
            }
        }
        return goodIndices;
    }
    
    private boolean checkGoodIndex(int[] nums, int idx, int k) {
        for (int j = 1; j <= k; j++) {
            if (nums[idx - j] < nums[idx - j + 1] || nums[idx + j] < nums[idx + j - 1]) {
                return false;
            }
        }
        return true;
    }
}

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