34. Find the Element in Sorted Array

Question

Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.

If target is not found in the array, return [-1, -1].

You must write an algorithm with O(log n) runtime complexity.

Solution

二分搜索，首先搜索target。如果搜索到结果为负数，则返回[-1, -1]。
如果搜索到target，则记录index。
然后从index向两边搜索，直到找到界限并返回。

Code

class Solution {
    public int[] searchRange(int[] nums, int target) {
        int[] ret = new int[2];
        int index = 0;
        index = Arrays.binarySearch(nums, target);
        if(index < 0){
            ret[0] = -1;
            ret[1] = -1;
            return ret;
        }
        int less = index, more = index;
        while(less >= 0 && nums[less] == target) less--;
        while(more < nums.length && nums[more] == target) more++;
        
        ret[0] = less + 1;
        ret[1] = more - 1;
        return ret;
    }
}