196.Find the Missing Number

public class Solution {
/**    
 * @param nums: an array of integers
 * @return: an integer
 */
public int findMissing(int[] nums) {
    // write your code here
    Arrays.sort(nums);
    int N = nums.length;
    int start = 0;
    int end = N - 1;
    while (start + 1 < end) {
        int mid = start + (end - start) / 2;
        if (nums[mid] > mid) end = mid;
        else start = mid;
    }
     if (nums[start] != start) return start;
    else if (nums[end] != end) return end;
    else return end + 1;
}
}


public class Solution {
/**    
 * @param nums: an array of integers
 * @return: an integer
 */
public int findMissing(int[] nums) {
    // write your code here
    int N = nums.length;
    int sum = 0;
    for (int i = 0; i < N; i++) {
        sum += nums[i];
    }
    
    return N * (N + 1) /2 - sum;
}
}


public class Solution {
/**    
 * @param nums: an array of integers
 * @return: an integer
 */
public int findMissing(int[] nums) {
    // write your code here
    Arrays.sort(nums);
    int N = nums.length;
    int start = 0;
    int end = N - 1;
    while (start + 1 < end) {
        int mid = start + (end - start) / 2;
        if (nums[mid] > mid) end = mid;
        else start = mid;
    }
     if (nums[start] != start) return start;
    else if (nums[end] != end) return end;
    else return end + 1;
}
}