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Merged
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Nov 14, 2020
Merged

Add dynamic programming top down approach for 72 #134

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43 changes: 43 additions & 0 deletions src/main/java/com/fishercoder/solutions/_72.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
package com.fishercoder.solutions;

import java.util.Arrays;

public class _72 {

public static class Solution1 {
Expand Down Expand Up @@ -35,4 +37,45 @@ public int minDistance(String word1, String word2) {
return table[m][n];
}
}
public static class Solution2{
public int minDistance(String word1, String word2) {
// using levenshtein Distance to find minimum transformation operations required from word 1 to word 2
int[][] dp = new int[word1.length()][word2.length()];
// fill the dp array with -1 value
for(int [] rows : dp){
Arrays.fill(rows, -1);
}
return levenshteinDistance(word1, word1.length()-1 , word2, word2.length()-1, dp);
}
private int levenshteinDistance( String s1, int s1Index, String s2, int s2Index, int[][] dp){

if(s1Index < 0){ // when s1 is "" perform all insertions to get s1 to s2
return s2Index + 1;
}
else if(s2Index < 0) { // when s2 is "" perform all deletions from s1
return s1Index + 1;
}

// base condition when dp array is filled, return the distance
if(dp[s1Index][s2Index] != -1)
return dp[s1Index][s2Index];

if(s1.charAt(s1Index) == s2.charAt(s2Index)){
// Characters match, no edit distance to be calculated
dp[s1Index][s2Index] = levenshteinDistance(s1, s1Index - 1, s2, s2Index - 1, dp);
}
else{
// When there is a character mismatch, perform operations

// Insertion
int insertValue = levenshteinDistance(s1, s1Index, s2, s2Index - 1, dp);
int deleteValue = levenshteinDistance(s1, s1Index - 1, s2, s2Index, dp);
int substituteValue = levenshteinDistance(s1, s1Index - 1, s2, s2Index - 1, dp);

/* Now we need to take the minimum of the 3 operations to find the edit distance and add 1 to the min cost action denoting that an action is performed */
dp[s1Index][s2Index] = 1 + Math.min(insertValue, Math.min(deleteValue, substituteValue));
}
return dp[s1Index][s2Index];
}
}
}
9 changes: 8 additions & 1 deletion src/test/java/com/fishercoder/_72Test.java
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Expand Up @@ -8,14 +8,21 @@

public class _72Test {
private static _72.Solution1 solution1;
private static _72.Solution2 solution2;


@BeforeClass
public static void setup() {
solution1 = new _72.Solution1();
solution1 = new _72.Solution1(); solution2 = new _72.Solution2();
}

@Test
public void test1() {
assertEquals(1, solution1.minDistance("Ada", "Adam"));
}

@Test
public void test2() {
assertEquals(5, solution1.minDistance("Ashmi", "Chheda"));
}
}