洛谷P1183 多边形的面积

深搜灌水 +  皮克定理

#include <bits/stdc++.h> 
#define For(i,j,k) for(int i=j;i<=k;i++)
#define LL long long 
using namespace std ; 

struct point{
    int x,y ; 
}p[111] ; 
int n,tmp[211][411],mp[211][411],a,b,s ; 
 
inline LL read() 
{
    LL x = 0 , f = 1 ; 
    char ch = getchar() ; 
    while(ch<'0'||ch>'9') { if(ch=='-') f = -1 ; ch = getchar() ; } 
    while(ch>='0'&&ch<='9') { x = x * 10+ch-48 ; ch = getchar() ; } 
    return x * f ;  
}

inline void dfs(int x,int y) 
{
    if(mp[x][y]) return ; 
    mp[x][y] = 1 ,b++ ; 
    dfs(x+1,y) ; dfs(x,y+1) ; 
    dfs(x-1,y) ; dfs(x,y-1) ; 
}

int main() 
{
    n = read() ; 
    For(i,1,n) {
        p[ i ].x = read() ; 
        p[ i ].y = read() ; 
    }
    p[n+1] = p[1] ; 
    For(i,1,n) {
        if(p[i].x==p[i+1].x) {
            a+=abs(p[i+1].y-p[i].y) ; 
            For(j,min(p[i].y,p[i+1].y),max(p[i].y,p[i+1].y)) 
                mp[p[i].x][j] = 1 ; 
        }
        else{
            a+=abs(p[i+1].x-p[i].x) ; 
            For(j,min(p[i].x,p[i+1].x),max(p[i].x,p[i+1].x)) 
                mp[j][p[i].y] = 1 ; 
        }
    } 
    dfs( p[1].x+1,p[1].y+1 ) ; 
    printf("%d
",a/2+b-1) ; 
    return 0 ; 
}