不同的結果VS C++和GNU G ++

Question

我有一個程序，在VS C++的工作，不與G ++工作。這裏是代碼：

#define _USE_MATH_DEFINES 

#include <cmath> 
#include <iostream> 
#include <vector> 
#include <cstdio> 
#include <algorithm> 
#include <set> 

#define EP 1e-10 

using namespace std; 

typedef pair<long long, long long> ii; 
typedef pair<bool, int> bi; 
typedef vector<ii> vii; 

// Returns the orientation of three points in 2D space 
int orient2D(ii pt0, ii pt1, ii pt2) 
{ 
    long long result = (pt1.first - pt0.first)*(pt2.second - pt0.second) 
     - (pt1.second - pt0.second)*(pt2.first - pt0.first); 
    return result == 0 ? 0 : result < 0 ? -1 : 1; 
} 

// Returns the angle derived from law of cosines center-pt1-pt2. 
// Defined to be negative if pt2 is to the right of segment pt1 to center 
double angle(ii center, ii pt1, ii pt2) 
{ 
    double aS = pow(center.first - pt1.first, 2) + pow(center.second - pt1.second, 2); 
    double bS = pow(pt2.first - pt1.first, 2) + pow(pt2.second - pt1.second, 2); 
    double cS = pow(center.first - pt2.first, 2) + pow(center.second - pt2.second, 2); 

/* long long aS = (center.first - pt1.first)*(center.first - pt1.first) + (center.second - pt1.second)*(center.second - pt1.second); 
    long long bS = (pt2.first - pt1.first)*(pt2.first - pt1.first) + (pt2.second - pt1.second)*(pt2.second - pt1.second); 
    long long cS = (center.first - pt2.first)*(center.first - pt2.first) + (center.second - pt2.second)*(center.second - pt2.second);*/ 

    int sign = orient2D(pt1, center, pt2); 

    return sign == 0 ? 0 : sign * acos((aS + bS - cS)/((sqrt(aS) * sqrt(bS) * 2))); 
} 

// Computes the average point of the set of points 
ii centroid(vii &pts) 
{ 
    ii center(0, 0); 
    for (int i = 0; i < pts.size(); ++i) 
    { 
     center.first += pts[i].first; 
     center.second += pts[i].second; 
    } 

    center.first /= pts.size(); 
    center.second /= pts.size(); 

    return center; 
} 

// Uses monotone chain to convert a set of points into a convex hull, ordered counter-clockwise 
vii convexHull(vii &pts) 
{ 
    sort(pts.begin(), pts.end()); 
    vii up, dn; 
    for (int i = 0; i < pts.size(); ++i) 
    { 
     while (up.size() > 1 && orient2D(up[up.size()-2], up[up.size()-1], pts[i]) >= 0) 
      up.pop_back(); 
     while (dn.size() > 1 && orient2D(dn[dn.size()-2], dn[dn.size()-1], pts[i]) <= 0) 
      dn.pop_back(); 

     up.push_back(pts[i]); 
     dn.push_back(pts[i]); 
    } 

    for (int i = up.size()-2; i > 0; --i) 
    { 
     dn.push_back(up[i]); 
    } 

    return dn; 
} 

// Tests if a point is critical on the polygon, i.e. if angle center-qpt-polygon[i] 
// is larger (smaller) than center-qpt-polygon[i-1] and center-qpt-polygon[i+1]. 
// This is true iff qpt-polygon[i]-polygon[i+1] and qpt-polygon[i]-polygon[i-1] 
// are both left turns (min) or right turns (max) 
bool isCritical(vii &polygon, bool mx, int i, ii qpt, ii center) 
{ 
    int ip1 = (i + 1) % polygon.size(); 
    int im1 = (i + polygon.size() - 1) % polygon.size(); 

    int p1sign = orient2D(qpt, polygon[i], polygon[ip1]); 
    int m1sign = orient2D(qpt, polygon[i], polygon[im1]); 

    if (p1sign == 0 && m1sign == 0) 
    { 
     return false; 
    } 

    if (mx) 
    { 
     return p1sign <= 0 && m1sign <= 0; 
    } 
    else 
    { 
     return p1sign >= 0 && m1sign >= 0; 
    } 
} 

// Conducts modified binary search on the polygon to find tangent lines in O(log n) time. 
// This is equivalent to finding a max or min in a "parabola" that is rotated and discrete. 
// Vanilla binary search does not work and neither does vanilla ternary search. However, using 
// the fact that there is only a single max and min, we can use the slopes of the points at start 
// and mid, as well as their values when compared to each other, to determine if the max or min is 
// in the left or right section 
bi find_tangent(vii &polygon, bool mx, ii qpt, int start, int end, ii center) 
{ 
    // When query is small enough, iterate the points. This avoids more complicated code dealing with the cases not possible as 
    // long as left and right are at least one point apart. This does not affect the asymptotic runtime. 
    if (end - start <= 4) 
    { 
     for (int i = start; i < end; ++i) 
     { 
      if (isCritical(polygon, mx, i, qpt, center)) 
      { 
       return bi(true, i); 
      } 
     } 

     return bi(false, -1); 
    } 

    int mid = (start + end)/2; 

    // use modulo to wrap around the polygon 
    int startm1 = (start + polygon.size() - 1) % polygon.size(); 
    int midm1 = (mid + polygon.size() - 1) % polygon.size(); 

    // left and right angles 
    double startA = angle(center, qpt, polygon[start]); 
    double midA = angle(center, qpt, polygon[mid]); 

    // minus 1 angles, to determine slope 
    double startm1A = angle(center, qpt, polygon[startm1]); 
    double midm1A = angle(center, qpt, polygon[midm1]); 

    int startSign = abs(startm1A - startA) < EP ? 0 : (startm1A < startA ? 1 : -1); 
    int midSign = abs(midm1A - midA) < EP ? 0 : (midm1A < midA ? 1 : -1); 

    bool left = true; 
    // naively 27 cases: left and left angles can be <, ==, or >, 
    // slopes can be -, 0, or +, and each left and left has slopes, 
    // 3 * 3 * 3 = 27. Some cases are impossible, so here are the remaining 18. 
    if (abs(startA - midA) < EP) 
    { 
     if (startSign == -1) 
     { 
      left = !mx; 
     } 
     else 
     { 
      left = mx; 
     } 
    } 
    else if (startA < midA) 
    { 
     if (startSign == 1) 
     { 
      if (midSign == 1) 
      { 
       left = false; 
      } 
      else if (midSign == -1) 
      { 
       left = mx; 
      } 
      else 
      { 
       left = false; 
      } 
     } 
     else if (startSign == -1) 
     { 
      if (midSign == -1) 
      { 
       left = true; 
      } 
      else if (midSign == 1) 
      { 
       left = !mx; 
      } 
      else 
      { 
       left = true; 
      } 
     } 
     else 
     { 
      if (midSign == -1) 
      { 
       left = false; 
      } 
      else 
      { 
       left = true; 
      } 
     } 
    } 
    else 
    { 
     if (startSign == 1) 
     { 
      if (midSign == 1) 
      { 
       left = true; 
      } 
      else if (midSign == -1) 
      { 
       left = mx; 
      } 
      else 
      { 
       left = true; 
      } 
     } 
     else if (startSign == -1) 
     { 
      if (midSign == -1) 
      { 
       left = false; 
      } 
      else if (midSign == 1) 
      { 
       left = !mx; 
      } 
      else 
      { 
       left = false; 
      } 
     } 
     else 
     { 
      if (midSign == 1) 
      { 
       left = true; 
      } 
      else 
      { 
       left = false; 
      } 
     } 
    } 

    if (left) 
    { 
     return find_tangent(polygon, mx, qpt, start, mid+1, center); 
    } 
    else 
    { 
     return find_tangent(polygon, mx, qpt, mid, end, center); 
    } 
} 

int main(){ 
    int n, m; 
    cin >> n >> m; 

    vii rawPoints(n); 
    for (int i = 0; i < n; ++i) 
    { 
     cin >> rawPoints[i].first >> rawPoints[i].second; 
    } 

    vii polygon = convexHull(rawPoints); 
    set<ii> points(polygon.begin(), polygon.end()); 
    ii center = centroid(polygon); 

    for (int i = 0; i < m; ++i) 
    { 
     ii pt; 
     cin >> pt.first >> pt.second; 

     bi top = find_tangent(polygon, true, pt, 0, polygon.size(), center); 
     bi bot = find_tangent(polygon, false, pt, 0, polygon.size(), center); 

     // a query point is inside if it is collinear with its max (top) and min (bot) angled points, it is a polygon point, or if none of the points are critical 
     if (!top.first || orient2D(polygon[top.second], pt, polygon[bot.second]) == 0 || points.count(pt)) 
     { 
      cout << "INSIDE" << endl; 
     } 
     else 
     { 
      cout << polygon[top.second].first << " " << polygon[top.second].second << " " << polygon[bot.second].first << " " << polygon[bot.second].second << endl; 
     } 
    } 
} 

我懷疑angle函數有什麼問題。我已經縮小到或者find_tangent。當我在angle函數中從double切換到long long時，我也在g ++中看到不同的結果。 double結果更接近正確，但我不明白爲什麼它應該有任何不同。我輸入的值很小，沒有溢出/舍入應該引起問題。當我分配給雙精度時，我也看到了在做pow(x, 2)或x*x時的差異。我不明白爲什麼這會有所作爲。

任何幫助，將不勝感激！

編輯：這裏是輸入文件：https://github.com/brycesandlund/Coursework/blob/master/Java/PrintPoints/points.txt

這裏是正確的結果： https://github.com/brycesandlund/Coursework/blob/master/CompGeo/CompGeo/correct.txt

這裏是不正確的結果： https://github.com/brycesandlund/Coursework/blob/master/CompGeo/CompGeo/fast.txt

Answer 1

的問題是與這一段代碼：

// Computes the average point of the set of points 
ii centroid(vii &pts) 
{ 
    ii center(0LL, 0LL); 
    for (int i = 0; i < pts.size(); ++i) 
    { 
     center.first += pts[i].first; 
     center.second += pts[i].second; 
    } 

    center.first /= pts.size();  //right here!! 
    center.second /= pts.size(); 

    return center; 
} 

我不知道爲什麼，但g ++被取負center.first，使之成爲一個積極的，由無符號整數pts.size分割時溢出long long。通過將這些語句轉換爲：

center.first /= (long long)pts.size(); 
center.second /= (long long)pts.size(); 

g ++和VS C++的輸出匹配。