LeetCode 2774: Array Upper Bound Solution

Problem Explanation

Explanation

To find the upper bound of a target value in a sorted array, we can use a binary search approach. The idea is to search for the first occurrence of the target value in the array, and then return its index or the index before it in case the target value is not found.

Initialize start = 0 and end = n-1, where n is the number of elements in the array.
Perform a binary search:
- Calculate mid as the average of start and end.
- If array[mid] <= target, update start = mid + 1.
- Otherwise, update end = mid - 1.
After the binary search ends, return end if array[end] == target, or return end - 1 if array[end] < target.

Time Complexity: O(log n)
Space Complexity: O(1)

Solution Code

class Solution {
    public int upperBound(int[] array, int target) {
        int start = 0;
        int end = array.length - 1;

        while (start <= end) {
            int mid = start + (end - start) / 2;
            if (array[mid] <= target) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
        }

        return (end >= 0 && array[end] == target) ? end : (end - 1);
    }
}

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2774. Array Upper Bound