Swap Characters Once to Minimize Differences - Google Top Interview Questions


Problem Statement :


You are given two lowercase alphabet strings s and t of the same length.

Given that you can make at most one swap between two characters in s, return the minimum number of indices where s[i] ≠ t[i].

Constraints

1 ≤ n ≤ 100,000 where n is the length of s and t

Example 1

Input

s = "abbz"

t = "zcca"

Output

2

Explanation

We can swap "a" and "z" to turn s into "zbba". Then there's 2 characters that differ between t.


Example 2

Input
s = "zfba"

t = "zbca"

Output

1

Explanation

We can swap "f" and "b" to turn s into "zbfa". Then there's only 1 character that differ between t.



Example 3

Input

s = "abc"

t = "abc"

Output

0

Explanation

We don't need to swap since all the characters in s already match with t.


Solution :



title-img 




                        Solution in C++ :

const int Z = 26;

int mismatched[Z];

int solve(string s, string t) {
    memset(mismatched, 0, sizeof(mismatched));
    int mismatched_pairs = 0;
    for (int i = 0; i < (int)s.size(); i++) {
        mismatched_pairs += s[i] != t[i];
        if (s[i] != t[i]) mismatched[s[i] - 'a'] |= 1 << (t[i] - 'a');
    }

    bool can_swap_one = false;
    for (int i = 0; i < Z; i++) {
        if (!mismatched[i]) continue;
        int i_bit = 1 << i;
        for (int j = 0; j < Z; j++) {
            if ((mismatched[i] & (1 << j)) && (mismatched[j] & i_bit)) return mismatched_pairs - 2;
            can_swap_one |= mismatched[j] & i_bit;
        }
    }

    return mismatched_pairs - can_swap_one;
}
                    


                        Solution in Java :

import java.util.*;

class Solution {
    public int solve(String a, String b) {
        int N = a.length();
        boolean[][] occ = new boolean[26][26];
        int ans = 0;
        boolean[] inA = new boolean[26];
        boolean[] inB = new boolean[26];
        for (int i = 0; i < N; i++) {
            int v1 = a.charAt(i) - 'a';
            int v2 = b.charAt(i) - 'a';
            if (v1 != v2) {
                ans++;
                occ[v1][v2] = true;
                inA[v1] = true;
                inB[v2] = true;
            }
        }
        for (int i = 0; i < 26; i++) {
            for (int j = i + 1; j < 26; j++) {
                if (occ[i][j] && occ[j][i]) {
                    // there exists indices where letters i and j can be swapped.
                    return ans - 2;
                }
            }
        }

        for (int i = 0; i < 26; i++) {
            if (inA[i] && inB[i]) {
                // a swap exists to get a pair of letter i.
                return ans - 1;
            }
        }

        return ans;
    }
}
                    


                        Solution in Python : 
                            
class Solution:
    def solve(self, s, t):
        badpairs = set()
        ans = 0
        for (a, b) in zip(s, t):
            if a == b:
                continue
            badpairs.add((a, b))
            ans += 1
        for x, y in badpairs:
            if (y, x) in badpairs:
                return ans - 2
        for x, _ in badpairs:
            for ch in ascii_lowercase:
                if (ch, x) in badpairs:
                    return ans - 1
        return ans


View More Similar Problems

Is This a Binary Search Tree?

For the purposes of this challenge, we define a binary tree to be a binary search tree with the following ordering requirements: The data value of every node in a node's left subtree is less than the data value of that node. The data value of every node in a node's right subtree is greater than the data value of that node. Given the root node of a binary tree, can you determine if it's also a

View Solution →

Square-Ten Tree

The square-ten tree decomposition of an array is defined as follows: The lowest () level of the square-ten tree consists of single array elements in their natural order. The level (starting from ) of the square-ten tree consists of subsequent array subsegments of length in their natural order. Thus, the level contains subsegments of length , the level contains subsegments of length , the

View Solution →

Balanced Forest

Greg has a tree of nodes containing integer data. He wants to insert a node with some non-zero integer value somewhere into the tree. His goal is to be able to cut two edges and have the values of each of the three new trees sum to the same amount. This is called a balanced forest. Being frugal, the data value he inserts should be minimal. Determine the minimal amount that a new node can have to a

View Solution →

Jenny's Subtrees

Jenny loves experimenting with trees. Her favorite tree has n nodes connected by n - 1 edges, and each edge is ` unit in length. She wants to cut a subtree (i.e., a connected part of the original tree) of radius r from this tree by performing the following two steps: 1. Choose a node, x , from the tree. 2. Cut a subtree consisting of all nodes which are not further than r units from node x .

View Solution →

Tree Coordinates

We consider metric space to be a pair, , where is a set and such that the following conditions hold: where is the distance between points and . Let's define the product of two metric spaces, , to be such that: , where , . So, it follows logically that is also a metric space. We then define squared metric space, , to be the product of a metric space multiplied with itself: . For

View Solution →

Array Pairs

Consider an array of n integers, A = [ a1, a2, . . . . an] . Find and print the total number of (i , j) pairs such that ai * aj <= max(ai, ai+1, . . . aj) where i < j. Input Format The first line contains an integer, n , denoting the number of elements in the array. The second line consists of n space-separated integers describing the respective values of a1, a2 , . . . an .

View Solution →