POJ 1654 (平面几何 多边形面积 水~)

题目链接:点击这里

题意:求多边形的面积.

就输出处理一下就好了.

#include <cstdio>#include <cmath>#include <algorithm>#include <iostream>#include <vector>#include <cstring>using namespace std;const int eps = 1e-8;const int INF = 1e20;const int pi = acos (-1.0);int dcmp (int x) {    if (fabs (x) < eps) return 0;    return (x < 0 ? -1 : 1);}inline int sqr (int x) {return x*x;}//*************点struct Point {    int x, y;    Point (int _x = 0, int _y = 0):x(_x), y(_y) {}    void input () {scanf ("%lf%lf", &x, &y);}    void output () {printf ("%.2f %.2f\n", x, y);}    bool operator == (const Point &b) const {        return (dcmp (x-b.x) == 0 && dcmp (y-b.y) == 0);    }    bool operator < (const Point &b) const {        return (dcmp (x-b.x) == 0 ? dcmp (y-b.y) < 0 : x < b.x);    }    Point operator + (const Point &b) const {        return Point (x+b.x, y+b.y);    }    Point operator - (const Point &b) const {        return Point (x-b.x, y-b.y);    }    Point operator * (int a) {        return Point (x*a, y*a);    }    Point operator / (int a) {        return Point (x/a, y/a);    }    int len2 () {//返回长度的平方        return sqr (x) + sqr (y);    }    int len () {//返回长度        return sqrt (len2 ());    }};int cross (Point a, Point b) {//叉积    return 1LL*a.x*b.y-1LL*a.y*b.x;}//*************多边形double polygon_area (Point *p, int n) {//多边形的有向面积,加上绝对值就是面积    //n个点    double area = 0;    for (int i = 1; i < n-1; i++) {        area += cross (p[i]-p[0], p[i+1]-p[0]);    }    return area/2;}#define maxn 1000005Point p[maxn];int n;char s[maxn];int main () {    int t;    cin >> t;    while (t--) {        scanf ("%s", s);        n = strlen (s); n--;        if (n == 0 || n == 2) {            printf ("0\n");            continue;        }        n--;        int len = 0;        p[len++] = Point (0, 0);        for (int i = 0; i < n; i++) {            if (s[i] == '8') p[len++] = p[len-1]+Point (0, 1);            if (s[i] == '7') p[len++] = p[len-1]+Point (-1, 1);            if (s[i] == '9') p[len++] = p[len-1]+Point (1, 1);            if (s[i] == '4') p[len++] = p[len-1]+Point (-1, 0);            if (s[i] == '6') p[len++] = p[len-1]+Point (1, 0);            if (s[i] == '1') p[len++] = p[len-1]+Point (-1, -1);            if (s[i] == '2') p[len++] = p[len-1]+Point (0, -1);            if (s[i] == '3') p[len++] = p[len-1]+Point (1, -1);        }        double ans = fabs (polygon_area (p, len))*2+eps;        long long res = (long long)ans;        printf ("%lld%s\n", res/2, (res&1 ? ".5" : ""));    }    return 0;}