用EasyX绘制多球碰撞中的碰撞代码

float minDistances2[BallNum][2]; // 记录某个小球，距离它最近的小球的距离，这个小球的下标        for (i=0;i<BallNum;i++)        {            minDistances2[i][0] = 9999999;            minDistances2[i][1] = -1;        }        // 求解所有小球两两之间的距离平方        for (i=0;i<BallNum;i++)        {            for (j=0;j<BallNum;j++)            {                if (i!=j) // 自己和自己不需要比                {                    float dist2;                    dist2 = (ball_x[i] - ball_x[j])*(ball_x[i] - ball_x[j])                        + (ball_y[i] - ball_y[j])*(ball_y[i] - ball_y[j]);                    if (dist2<minDistances2[i][0])                    {                        minDistances2[i][0] = dist2;                        minDistances2[i][1] = j;                    }                }            }        }           // 判断球之间是否碰撞        for (i=0;i<BallNum;i++)        {            if (minDistances2[i][0]<=4*radius*radius) // 最小距离小于阈值，发生碰撞            {                j = minDistances2[i][1];                // 交换速度                             int temp;                temp = ball_vx[i]; ball_vx[i] = ball_vx[j]; ball_vx[j] = temp;                temp = ball_vy[i]; ball_vy[i] = ball_vy[j]; ball_vy[j] = temp;                minDistances2[j][0] = 999999999; // 避免交换两次速度，又回去了                minDistances2[j][1] = -1;            }        }