HDU 1391 number steps（找規律，數學）

Starting from point (0,0) on a plane, we have written all non-negative integers 0, 1, 2,... as shown in the figure. For example, 1, 2, and 3 has been written at points (1,1), (2,0), and (3, 1) respectively and this pattern has continued. 

You are to write a program that reads the coordinates of a point (x, y), and writes the number (if any) that has been written at that point. (x, y) coordinates in the input are in the range 0...5000. 

3
4 2
6 6
3 4      

6
12
No Number      

#include<iostream>
#include<stdio.h>
#include<algorithm>
using namespace std;
int main()
{
    int t;
    int x,y;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d%d",&x,&y);
        if(x==y+2||x==y)//2條線所在
        {
            if(x%2==1)//分奇偶找規律
            printf("%d\n",(x+y)-1);
        else if(x%2==0)
            printf("%d\n",x+y);
        }
        else
            printf("No Number\n");
    }
    return 0;
}