[leetcode]35. Search Insert Position寻找插入位置

Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.

You may assume no duplicates in the array.

Example 1:

Input: [1,3,5,6], 5
Output: 2

Example 2:

Input: [1,3,5,6], 2
Output: 1

Example 3:

Input: [1,3,5,6], 7
Output: 4

Example 4:

Input: [1,3,5,6], 0
Output: 0

 

题意：

给定有序数组和一个target，寻找合适的插入位置。

 

Solution1: Binary Search

数组元素有偶数个时， 中点若取偏左端的那个

1 　　2 　　3 　　4

        ^mid

那么，更新left时，从mid + 1 开始

 

code:

/*
Time: O(log(n))
Space: O(1)
*/
class Solution {
   public int searchInsert(int[] nums, int target) {
        //corner case
        if (nums == null || nums.length == 0) {
            return 0;
        }
        if (target < nums[0]) {   //[1,3,5,6], 0
            return 0;
        } else if (target > nums[nums.length - 1]) {  // [1,3,5,6], 7
            return nums.length;
        }
        // binary search
        int left = 0, right = nums.length - 1;
        while (left < right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] == target) {
                return mid;
            } else if (nums[mid] > target) {
                right = mid;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }
}