sicily 1047. Super Snooker

#include <iostream>            //因为有多个样例N ≤ 10000,所以对 连续数[low,high] 直接套用 0-1背包会TLE
#include<stdio.h>
using namespace std;
int main() 
{ 
    int cases,a,b,low,high;
    cin>>cases;
    while(cases--)
    {
        cin>>a>>b>>low>>high;
        if(a>b)
            swap(a,b);    //假定a<b
        int s=(low+high)*(high-low+1)/2;
        if((a+b+s)%2==1||b>a+s||(s+b-a)%2==1)    //(s+b-a)%2==0才能保证下面的 x 是整数
        {
            printf("not possible\n");
        }
        else
        {
            int x=(s+b-a)/2;    //a+x=b+s-x
            int tag=0,m,n;
            for(int len=1;len<=high-low+1;++len)    // x 由 len个在[low,high]内的数组成
            {
                m=(low+low+len-1)*len/2;n=(high-len+1+high)*len/2;        //m=low+..+low+len-1  n=high-len+1+...+high
                if(m<=x&&x<=n)        //因为是连续数,所以 len 个在[low,high]内的数的和 必然是在[m,n]内,故只要 x 落在该范围内,则组合成功
                {
                    tag=1;    break;
                }
            }
            if(tag==1)
                printf("possible\n");
            else
                printf("not possible\n");
        }
    }
    return 0;
}