Article directory
1. Title
Magic Index. In arrays A[0...n-1], there are so-called magic indexes, which satisfy conditions A[i] = i. Given a sorted array of integers, write a method to find the magic index in array A, if any, and return -1 if there is none. If there are multiple magic indexes, the one with the smallest index value is returned.
Example 1:
Input: nums = [0, 2, 3, 4, 5]
Output: 0
Description: The element with subscript 0 is 0
Example 2:
Input: nums = [1, 1, 1]
Output: 1
illustrate:
- The length of nums is between [1, 1000000]
- This title is Follow-up in the original book, which is a version in which the array may contain duplicate elements.
Click here to jump to the question .
2. C# problem solution
Traverse in sequence, but prune: if the current value is greater than the index, jump to the index position of the current value.
public class Solution {
public int FindMagicIndex(int[] nums) {
if (nums[0] > nums.Length || nums[^1] < 0) return -1;
int i = 0;
while (i < nums.Length) {
if (nums[i] == i) return i; // 找到魔术索引，立即返回
if (nums[i] > i) i = nums[i]; // 如果当前值大于索引，则跳转到当前值的索引位置
else i++; // 否则，继续判断下一个位置
}
return -1;
}
}
- Time: 88 ms, beating 81.82% of users using C#
- Memory: 41.7 MB, beats 72.73% of users using C#