1. Understanding the Basic Structure
Python Source Code:
total = 0
for i in range(1, 15, 3):
for j in range(1, i, 2):
if i * j % 2 == 0:
break
else:
total += i
print(total)
'''
i (1, 4, 7, 10, 13)
i = 1 j range(1,1,2) = ()
i = 4 j range(1,4,2) = (1,3)
i = 7 j range(1,7,2) = (1,3,5)
i = 10 j range(1,10,2) = (1,3,5,7, 9)
i = 13 j range(1,13,2) = (1,3,5,7,9,11)
'''
This Python code demonstrates a classic nested loop problem. It initializes a variable total to 0, then enters an outer loop using range(1,15,3) which generates the sequence [1,4,7,10,13]. For each i value, an inner loop uses range(1,i,2) to create odd number sequences. The inner loop breaks if i*j is divisible by 2, otherwise it adds i to total. The final output is 99.
2. Analyzing Outer Loop Variables
The range of outer loop i values is crucial. range(1,15,3) produces five values: 1,4,7,10,13. When i=1, the inner range(1,1,2) is empty; i=4 produces [1,3]; i=7 gives [1,3,5]; i=10 generates [1,3,5,7,9]; and i=13 creates [1,3,5,7,9,11].
3. Inner Loop Logic Breakdown
The core of inner loop is the condition i*j%2==0. When true, it breaks immediately. Otherwise, it adds current i to total. For example, when i=4 and j=1, 4*1%2=0 causes break, keeping total at 0. With i=7, none of the three iterations meet the condition, so it adds 7 three times, making total 21.
4. Building Variable Tracking Tables
The most effective analysis method is creating tracking tables. The first row records i values, the second shows corresponding j sequences, the third indicates break conditions, and the fourth tracks total changes. This reveals: i=1 does nothing; i=4 breaks; i=7 adds 7 three times; i=10 breaks immediately; i=13 adds 13 six times. Final calculation: 0+0+21+0+78=99.
5. Universal Problem-Solving Approach
This case demonstrates a universal method for analyzing nested loops: 1) Identify loop ranges; 2) Find inter-loop relationships; 3) Create variable tracking tables; 4) Simulate execution step-by-step. This approach is particularly valuable for exams or interviews when you can’t actually run the code.
6. Demo Video
You can watch the following demo video by select the subtitle to your preferred subtitle language.