[数据结构与算法]LeetCode#704. Binary Search

704. Binary Search

难度：简单
来源：LeetCode

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

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

Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

Constraints:

• 1 <= nums.length <= 104
• -104 < nums[i], target < 104
• All the integers in nums are unique.
• nums is sorted in ascending order.

二分查找

class Solution {
    public int search(int[] nums, int target) {
        int a = 0;
        int b = nums.length - 1;
        while (a <= b) {
            int n = (a + b) / 2;
            if (nums[n] > target) {
                b-=1;
            } else if (nums[n] < target) {
                a+=1;
            } else {
                return n;
            }
        }
        return -1;
    }
}