153 Find Minimum in Rotated Sorted Array

1. Question

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.
(i.e.,0 1 2 4 5 6 7might become4 5 6 7 0 1 2).
Find the minimum element.
You may assume no duplicate exists in the array.

2. Implementation

(1) Binary Search
思路:用二分查找,每次取中点,比较nums[mid] 和 nums[end]的大小关系,如果nums[mid] > nums[end], 说明最小值一定在[mid + 1, end]之间,否则最小值在[start, mid - 1]之间
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class Solution {
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public int findMin(int[] nums) {
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int start = 0, end = nums.length - 1, mid = 0;
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while (start + 1 < end) {
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mid = start + (end - start) / 2;
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if (nums[mid] > nums[end]) {
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start = mid + 1;
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}
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else {
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end = mid;
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}
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}
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return nums[start] < nums[end] ? nums[start] : nums[end];
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}
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}
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3. Time & Space Complexity

时间复杂度O(logn), 空间复杂度O(1)