By Long Luo

This article is the solution Java Binary Search Solution of Problem 278. First Bad Version.

Intuition

We can use Binary Search method to exclusive a half to reduce the scale Each Round.

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public int firstBadVersion(int n) {
        int left = 1;
        int right = n;

        while (left < right) {
            int mid = left + (right - left) / 2;
            if (isBadVersion(mid)) {
                right = mid;
            } else {
                left = mid + 1;
            }
        }

        return left;  
    }

Analysis

• Time Complexity: \(O(\log n)\).
• Space Complexity: \(O(1)\).

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