LeetCode

Find Minimum in Rotated Sorted Array

 

Suppose a sorted array is rotated at some pivot unknown to you beforehand.

(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

Find the minimum element.

You may assume no duplicate exists in the array.  

該題仍然局部有序，仍然使用二分查找，只是判斷移動遊標的方式不一樣，另外針對{6,5,4,3,2,1}這種case ，需要特殊處理

public static int findMin(int[] num) {
		int start =  0 , end = num.length - 1;
		int result = 0;
		int key = (num[start] - num[end]);
		while(true){
			int mid = (start+end)/2;
			
			if((num[start] - num[mid]) * key > 0){
				//mid處於後半段
				end = mid;
			}else if((num[start] - num[mid]) * key < 0){
				//mid處於前半段
				start = mid;
			}else {
				//start ，end 都已經移動到最小值的位置
				if(key < 0){
					result = num[start];
				}else{
					result = num[end];
				}
				break;
			}
		}
		//對於 有序遞減 的Case，該算法將遊標移動到了最大值處，此時末尾即是最小值。
		return  (result < num[num.length - 1]) ? result:num[num.length - 1];
		
	}

Submission Result: Accepted