LeetCode 33. 搜索旋轉排序數組 二分

題意：給一個旋轉數組和一個目標值target，求用O(logn)時間在數組中找出target值
思路：首先用二分找到旋轉後的開始索引，之後根據目標值和兩個子數組大小關係在子數組中再用二分即可。注意找開始索引和找目標值用的二分方法不同

class Solution {
    public int search(int[] nums, int target) {
        if (nums.length == 0)
            return -1;
        int l = 0, r = nums.length-1, index = -1;
        while (l < r) {
            int mid = (l+r)>>1;
            if (nums[mid] > nums[r]) {
                l = mid + 1;
            } else {
                r = mid;
            }
        }
        index = l;
        if (nums[index] <= target && nums[nums.length-1] >= target) {
            l = index;r = nums.length-1;
            while (l <= r) {
                int mid = (l+r)>>1;
                if (nums[mid] > target) {
                    r = mid - 1;
                } else {
                    l = mid + 1;
                }
            }
        } else {
            l = 0;r = index - 1;
            while (l <= r) {
                int mid = (l+r)>>1;
                if (nums[mid] > target) {
                    r = mid - 1;
                } else {
                    l = mid + 1;
                }
            }
        }
        if (l >= 0 && l < nums.length && nums[l] == target) {
            return l;
        } else if (r >= 0 && r < nums.length && nums[r] == target) {
            return r;
        } else {
            return -1;
        }
    }
}