Lintcode14 First Position of Target Solution 题解

【题目描述】

For a given sorted array (ascending order) and a target number, find the first index of this number in O(log n) time complexity.

If the target number does not exist in the array, return -1.

给定一个排序的整数数组（升序）和一个要查找的整数target，用O(logn)的时间查找到target第一次出现的下标（从0开始），如果target不存在于数组中，返回-1。

【题目链接】

http://www.lintcode.com/en/problem/first-position-of-target/

【题目解析】

这题目要求O(logn)的复杂度，又是sorted array，话不多说我们来搞二分法。注意要求first position of target所以当(array[mid] == target)的时候，操作是end = mid。

二分查找到第一个target后使用逐个向前查询第一个target

全程使用二分查找

【答案链接】

http://www.jiuzhang.com/solutions/first-position-of-target/

转载于:https://blog.51cto.com/12799252/1919312

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