【算法】二分查找，LeetCode33. 搜索旋转排序数组题解

LeetCode33. 搜索旋转排序数组

class Solution {
    /**
        先找到非单调的分界点，
        然后在各自段进行二分查找
     */
    public int search(int[] nums, int target) {
        //4 5 6 7 0 1 2
        // 二分找到分界点0，然后在每段再各自二分

        int n = nums.length;
        int left = 0;
        int right = n - 1;
        while (left < right) {
            int mid = (left + right) / 2; // 0
            
            // 如果二分点恰好是目标值，直接返回
            if (nums[mid] == target) return mid;
            
            if (nums[mid] <= nums[n - 1]) {
                right = mid; // 0
            } else {
                left = mid + 1;
            }
        }

        if (nums[right] == target) {
            return right;
        } else if (nums[right] < target && target <= nums[n - 1]) {
            // 在右半段
            return binarySearch(nums, right + 1, n - 1, target);
        } else {
            return binarySearch(nums, 0, right - 1, target);
        }
    }

    // 起始 结束
    public int binarySearch(int[] nums, int start, int end, int target) {
        int left = start;
        int right = end;
        while (left <= right) {
            int mid = (left + right) / 2;
            if (nums[mid] == target) {
                return mid;
            }
            if (nums[mid] < target) { // 在右边
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }
        return -1;
    }
}