cf 156 div.2 D. Mr. Bender and Square

这题就是先算总面积，再减去超出面积，再加上重叠面积。关键要注意细节。

/*
author:jxy
lang:C/C++
university:China,Xidian University
**If you need to reprint,please indicate the source**
*/
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <queue>
#define INF 1E9
using namespace std;
int main()
{
    long long n,x,y,c;
    cin>>n>>y>>x>>c;
    long long now=0;
    long long i,xr,xl,yu,yd,d;
    x--;y--;
    for(i=1;now<c;i++)
    {
        now=i*i+(i-1)*(i-1);
        if(now<c)continue;
        i--;
        xr=x+i;
        xl=x-i;
        yu=y-i;
        yd=y+i;
        if(xl<0)now-=xl*xl;
        if(xr>n-1)now-=(xr-n+1)*(xr-n+1);
        if(yu<0)
        {
            now-=yu*yu;
            yu++;
            d=-yu;
            if(x+d>n-1)now+=(x+d-n+2)*(x+d-n+1)/2;
            if(x+yu<0)now+=(x-d)*(x-d-1)/2;
        }
        if(yd>n-1)
        {
            now-=(yd-n+1)*(yd-n+1);
            d=yd-n+1;
            d--;
            if(x+d>n-1)now+=(x+d-n+2)*(x+d-n+1)/2;
            if(x-d<0)now+=(x-d)*(x-d-1)/2;
        }
        i++;
    }
    cout<<i-2<<endl;
}