72. Edit Distance

Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.)

You have the following 3 operations permitted on a word:

a) Insert a character
b) Delete a character
c) Replace a character

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public class Solution {
    public int minDistance(String word1, String word2) {
      
        if(word1==null || word2==null)
            return 0;
        
        int n1 = word1.length();
        int n2 = word2.length();
        
        if(n1==0)   return n2;
        if(n1==0)   return n1;
        
        int[][] dist = new int[n1+1][n2+1];
        for(int i=0; i<=n1; i++){
            dist[i][0] = i;
        }
        for(int j=0; j<=n2; j++){
            dist[0][j] = j;
        }
        
        for(int i=0; i<n1; i++){
            int v1 = word1.charAt(i);
            for(int j=0; j<n2; j++){
                int v2 = word2.charAt(j);
                
                if(v1 == v2)
                    dist[i+1][j+1] = dist[i][j];
                else{
                    int min = Math.min(dist[i][j], dist[i][j+1]);
                    dist[i+1][j+1] = Math.min(dist[i+1][j],min) + 1;
                }
            }
        }
        
        return dist[n1][n2];
        
        
    }
}