lcb-0075

1.000

4/4 tests· algorithms

Proposed solution

I'll solve this step by step.

## Problem Understanding

1. We have two strings S and T of equal length N
2. We need to count how many positions have different characters between the two strings
3. This is exactly what Hamming distance measures

## Approach

1. Read N (length of strings)
2. Read string S
3. Read string T
4. Compare each character at position i from both strings
5. Count how many positions have different characters
6. Output the count

## Step-by-step Solution

Let me trace through Sample 1:
- N = 6
- S = "abcarc"
- T = "agcahc"
- Position 1: 'a' vs 'a' → same
- Position 2: 'b' vs 'g' → different (count = 1)
- Position 3: 'c' vs 'c' → same
- Position 4: 'a' vs 'h' → different (count = 2)
- Position 5: 'r' vs 'c' → different (count = 3)
- Position 6: 'c' vs 'c' → same
- Wait, let me recheck the sample... 

Actually, looking at the sample explanation:
- S = "abcarc" 
- T = "agcahc"
- 2nd character: 'b' vs 'g' → different
- 5th character: 'r' vs 'c' → different
- So positions 2 and 5 differ

## Implementation

```python
# Read input
N = int(input())
S = input().strip()
T = input().strip()

# Count differences
count = 0
for i in range(N):
    if S[i] != T[i]:
        count += 1

# Output result
print(count)
```

Let me verify with the examples:

Sample 1: N=6, S="abcarc", T="agcahc"
- i=0: 'a'=='a' → no difference
- i=1: 'b'!='g' → difference (count=1)
- i=2: 'c'=='c' → no difference  
- i=3: 'a'!='h' → difference (count=2)
- i=4: 'r'!='c' → difference (count=3)
- i=5: 'c'=='c' → no difference

Wait, that gives 3 differences but expected is 2. Let me re-read...

Actually, the problem says "the i-th character" and the sample shows positions 2 and 5 differ:
S = "abcarc" (positions 1,2,3,4,5,6)
T = "agcahc" (positions 1,2,3,4,5,6)

Position 1: 'a'=='a' ✓
Position 2: 'b'!='g' ✗
Position 3: 'c'=='c' ✓  
Position 4: 'a'!='h' ✗
Position 5: 'r'!='c' ✗
Position 6: 'c'=='c' ✓

That's 3 differences, but the sample says 2. Let me check again...

Looking more carefully at the problem statement:
"Find the Hamming distance between S and T. That is, find the number of integers i such that 1 ≤ i ≤ N and the i-th character of S is different from the i-th character of T."

The sample explanation says "S and T differ in the 2nd and 5th characters". Let me check:
- 2nd character: S[1]='b', T[1]='g' → different ✓
- 5th character: S[4]='r', T[4]='c' → different ✓

So it's 2 differences. But in my manual trace above I got 3. Let me recheck the strings:
S = "abcarc" (indices 0,1,2,3,4,5)
T = "agcahc" (indices 0,1,2,3,4,5)

Position 1: S[1]='b', T[1]='g' → different
Position 2: S[2]='c', T[2]='c' → same  
Position 3: S[3]='a', T[3]='h' → different
Position 4: S[4]='r', T[4]='c' → different
Position 5: S[5]='c', T[5]='c' → same

That's 3 differences. But the sample says 2. 

Wait, I think there might be an indexing issue in my understanding. Let me just implement and test:

```python
# Read input
N = int(input())
S = input().strip()
T = input().strip()

# Count differences
count = 0
for i in range(N):
    if S[i] != T[i]:
        count += 1

# Output result
print(count)
```

Test output (stdout)

....                                                                     [100%]
4 passed in 0.06s

System prompt

You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.