Some dwarves that are finishing the StUDY (State University for Dwarven Youngsters) Bachelor courses, have been told "no genome, no degree". That means that all dwarves should write a thesis on genome. Dwarven genome is far from simple. It is represented by a string that consists of lowercase Latin letters.

Dwarf Misha has already chosen the subject for his thesis: determining by two dwarven genomes, whether they belong to the same race. Two dwarves belong to the same race if we can swap two characters in the first dwarf‘s genome and get the second dwarf‘s genome as a result. Help Dwarf Misha and find out whether two gnomes belong to the same race or not.

The first line contains the first dwarf‘s genome: a non-empty string, consisting of lowercase Latin letters.

The second line contains the second dwarf‘s genome: a non-empty string, consisting of lowercase Latin letters.

The number of letters in each genome doesn‘t exceed 105. It is guaranteed that the strings that correspond to the genomes are different. The given genomes may have different length.

Print "YES", if the dwarves belong to the same race. Otherwise, print "NO".

先看長度等不等，不等直接no

等的情況下觀察兩個字符串有幾位是不一樣的，不為2就是no，為2的情況下換一下再比較試試看

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;


string s1,s2;

int main(){
  // freopen("test.in","r",stdin);
  cin >> s1 >> s2;
  int len = s1.length();
  if (len != s2.length()){
    cout << "NO"; return 0;
  }
  int total = 0,pos1 = 0,pos2 = 0;
  for (int i=0;i<len;i++){
    if (s1[i] != s2[i]){
      total ++;
      if (total == 1){
        pos1 = i;
      }
      else {
        pos2 = i;
      }
    }
  }
  if (total == 2 || total == 0){
    swap(s1[pos1],s1[pos2]);
    if (s1 == s2){
      cout << "YES";
    }
    else
      cout << "NO";
  }
  else
    cout << "NO";
}

Codeforces 186A. Comparing Strings