LeetCode 268. Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, …, n, find the one that is missing from the array.

For example,
Given nums = [0, 1, 3] return 2.

Note:
Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int *book = new int [nums.size() + 1];
        for(int i = 0; i <= nums.size(); i++) {
            book[i] = 0;
        }
        for(int i = 0; i < nums.size(); i++) {
            book[nums[i]] = 1;
        }
        for(int i = 0; i <= nums.size(); i++) {
            if(book[i] == 0) {
                return i;
            }
        }
    }
};

class Solution {

public:

int missingNumber(vector<int>& nums) {

int *book = new int [nums.size() + 1];

for(int i = 0; i <= nums.size(); i++) {

book[i] = 0;

}

for(int i = 0; i < nums.size(); i++) {

book[nums[i]] = 1;

}

for(int i = 0; i <= nums.size(); i++) {

if(book[i] == 0) {

return i;

}

};

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