Question

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

Solution

Solution 1: Binary Search

class Solution {
 public:
  int searchInsert(vector<int>& nums, int target) {
    if (nums.back() < target) return nums.size();
    int left = 0, right = nums.size() - 1;
    while (left < right) {
      int mid = left + (right - left) / 2;
      if (nums[mid] == target)
        return mid;
      else if (nums[mid] < target)
        left = mid + 1;
      else
        right = mid;
    }
    return right;
  }
};

Solution 2: Scan

class Solution {
 public:
  int searchInsert(vector<int>& nums, int target) {
    if (nums.empty()) return 0;
    for (int i = 0; i < nums.size(); ++i) {
      if (nums[i] >= target) return i;
    }
    return nums.size();
  }
};