LeetCode Problem 35:Search Insert Position-优快云博客

本文介绍了在已排序数组中查找目标值并确定其插入位置的两种方法：遍历法和二分查找法。遍历法简单直接，适用于小规模数据；二分查找法则效率更高，适用于大规模数据。

描述：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.

Here are few examples.
[1,3,5,6], 5 → 2
[1,3,5,6], 2 → 1
[1,3,5,6], 7 → 4
[1,3,5,6], 0 → 0

思路1：直观的想法，遍历数组，一旦当前元素>=target，当前元素的位置即为插入位置，边界问题处理一下即可。时间复杂度：O(n)

 1 class Solution {
 2 public:
 3     int searchInsert(int A[], int n, int target) {
 4 
 5         if(target > A[n-1])
 6             return n;
 7             
 8         else    {        
 9             for(int i = 0; i < n; i++)  {
10                 if(A[i] >= target)
11                     return i;
12             }
13         }
14     }
15 };

思路2：由于给定数组为已经排好序的，可以使用二分查找，比较A[mid]与target的大小。时间复杂度：O(logn)

 1 class Solution {
 2 public:
 3     int searchInsert(int A[], int n, int target) {
 4         
 5         int start = 0;
 6         int end = n - 1;
 7         int mid = 0;
 8         
 9         while(end >= start)  {
10             
11             mid = (start + end) / 2;
12             if(target == A[mid])
13                 return mid;
14             else if(target > A[mid])
15                 start = mid + 1;
16             else
17                 end = mid - 1;
18         }
19         
20         if(target > A[mid])
21             return mid + 1;
22         else
23             return mid;
24 
25     }
26 };