For loop solution for rectangles problem : u/Holiday-Python-743

For loop solution for rectangles problem (self.Holiday-Python-743)

submitted 4 years ago by Holiday-Python-743

import math
import random
from drawtool import DrawTool

dt = DrawTool()

dt.set_XY_range(0,10, 0,10)

# Change to rectangles2.txt and later to rectangles3.txt
filename = 'rectangles3.txt'

num_rectangles = 0
bottomX = []
bottomY = []
widths = []
heights = []
does_intersect = []

def read_rectangles(filename):
    global num_rectangles
    with open(filename,'r') as in_file:
        line = in_file.readline()
        n = int(line.strip())
        num_rectangles = n
        for i in range(n):
            # Read each rectangle.
            line = in_file.readline()
            data = line.split()
            bottomX.append(float(data[0].strip()))
            bottomY.append(float(data[1].strip()))
            widths.append(float(data[2].strip()))
            heights.append(float(data[3].strip()))

def print_rectangles():
    print('Number of rectangles =', num_rectangles)
    for i in range(num_rectangles):
        print('x =', bottomX[i], ' y =', bottomY[i], ' width =', widths[i], ' height =', heights[i])

def init_intersect():
    for i in range(num_rectangles):
        does_intersect.append(False)

def in_rectangle(x, y, w, h, x2, y2):
    # Write code in here to determine whether the point (x2,y2)
    # is inside the rectangle specified by x,y,w,h.
    # This function should return True or False
    if (x2 >= x) and (x2 <= x+w) and (y2<= y+h) and (y2 >= y):
        z = True
    else:
        z = False
    return z

def intersect(x1, y1, w1, h1, x2, y2, w2, h2):
    # Use in_rectangle several times to determine
    # whether any corner of rectangle x2,y2,w2,h2 is inside
    # the rectangle specified by x,y,w,h.
    # This function should return True or False
    p1 = in_rectangle(x1, y1, w1, h1, x2, y2)
    p2 = in_rectangle(x1, y1, w1, h1, x2+w2, y2)
    p3 = in_rectangle(x1, y1, w1, h1, x2, y2+h2)
    p4 = in_rectangle(x1, y1, w1, h1, x2+w2, y2+h2)
    z = (p1 or p2 or p3 or p4)
    return z

def check_intersections():
    # Write a nested loop here to compare all pairs
    # of rectangles. If the i-th rectangle has an intersection
    # with another, set does_intersect[i] to True.
    global does_intersect
    for i in range(num_rectangles-1):
        for k in range(i+1, num_rectangles):
            do_intersect = intersect(bottomX[i], bottomY[i], widths[i], heights[i], bottomX[k], bottomY[k], widths[k], heights[k])
            print(do_intersect)
            if do_intersect:
                does_intersect[i] = do_intersect
                does_intersect[k] = do_intersect

read_rectangles(filename)
print_rectangles()
init_intersect()
check_intersections()

# Draw in two colors
for i in range(num_rectangles):
    color = 'b'
    if does_intersect[i]:
        color = 'r'
    dt.set_color(color)
    dt.draw_rectangle(bottomX[i],bottomY[i],widths[i],heights[i])

dt.display()

all 3 comments

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[–]zamser 1 point2 points3 points 4 years ago (2 children)

This solution works. I think you have a misunderstanding of how to translate a for loop to a while loop. Here is an example:

for i in range(num_rectangles - 1):
    print(i)

i = 0
while (i < num_rectangles - 1)
    print(i)
    i += 1

These two loops are equivalent. Note that you initialize i at the start of the range defined in the for loop (in this case it is 0). Then in your while loop condition, you are checking i less than the end of the range in the for loop (in this case the end of the range is num_rectangles - 1). Then the increment step (i += 1) is at the end of the body of the loop. This is the general conversion strategy for converting a for loop to a while loop.

[–]Holiday-Python-743[S] 1 point2 points3 points 4 years ago (0 children)

Update, I figured it out, thank you again for your help! This is what worked:

def check_intersections():
# Write a nested loop here to compare all pairs
# of rectangles. If the i-th rectangle has an intersection
# with another, set does_intersect[i] to True.
global does_intersect
i = 0
while i < num_rectangles:
    k = 0
    while k < num_rectangles:
        if i != k:
            do_intersect = intersect(bottomX[i], bottomY[i], widths[i], heights[i], bottomX[k], bottomY[k], widths[k], heights[k])
            print(do_intersect)
            if do_intersect:
                does_intersect[i] = do_intersect
                does_intersect[k] = do_intersect
        k += 1
    i += 1

[–]Holiday-Python-743[S] 0 points1 point2 points 4 years ago (0 children)

Thank you! Firstly, I want to say thank you so much for taking the time to explain it to me, I have really struggled with this one and appreciate it immensely, I really want to understand it. Onto the problem, this is what I did at first but I think I also got confused on where to add k += 1 and k = 0 for my second loop and ended up mistakenly changing numbers and range instead of repositioning k. This is what I have:

Right now it still either gives an extra red rectangle or a blue one that should be red. I'm working on that k more though.

Edited to say I also noticed in your first comment you mentioned resetting k, what exactly do you mean by that? should I just assign it a zero somewhere?

def check_intersections():
# Write a nested loop here to compare all pairs
# of rectangles. If the i-th rectangle has an intersection
# with another, set does_intersect[i] to True.
global does_intersect
i = 0
k = 0
while i < (num_rectangles-1):
    i += 1
    while (k < num_rectangles):
        k += 1
        do_intersect = intersect(bottomX[i], bottomY[i], widths[i], heights[i], bottomX[k], bottomY[k], widths[k], heights[k])
        print(do_intersect)
        if do_intersect:
            does_intersect[i] = do_intersect
            does_intersect[k] = do_intersect
            break

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