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EditDistanceDP.java
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packagesection19_DynamicProgramming;
publicclassEditDistanceDP {
publicstaticvoidmain(String[] args) {
// String s1 = "abcd", s2 = "agcfd";
// String s1 = "saturday", s2 = "sunday";
// System.out.println(editDistanceRecursion(s1, s2)); // 2
// System.out.println(edRecursionVirtualIndex(s1, s2, 0, 0));
Strings1 = "adsfadfiaosdggahosdfasf", s2 = "asdfhoagihsadasdgihsdoif";
int[][] storage = newint[s1.length()][s2.length()];
for (introw = 0; row < storage.length; row++) {
for (intcol = 0; col < storage[1].length; col++) {
storage[row][col] = -1;
}
}
System.out.println(editDistanceTopDownDP(s1, s2, 0, 0, storage));
System.out.println(editDistanceBottomUpDP(s1, s2)); // 16
}
publicstaticinteditDistanceRecursion(Strings1, Strings2) {
// base case
if (s1.length() == 0) {
returns2.length();
}
if (s2.length() == 0) {
returns1.length();
}
charch1 = s1.charAt(0);
charch2 = s2.charAt(0);
Stringros1 = s1.substring(1);
Stringros2 = s2.substring(1);
intdistance = 0;
if (ch1 == ch2) {
distance = editDistanceRecursion(ros1, ros2);
} else {
intinsertion = editDistanceRecursion(ros1, s2);
intdeletion = editDistanceRecursion(s1, ros2);
intreplacement = editDistanceRecursion(ros1, ros2);
distance = 1 + Math.min(insertion, Math.min(deletion, replacement));
}
returndistance;
}
/*
* Recursive approach will fail for large inputs due to exponential time.
*
* without using substring method, using virtual index.
*
* O(3^(m+n)) Time, m is length of s1, n is length of s2 | recursion space
*
*/
publicstaticintedRecursionVirtualIndex(Strings1, Strings2, intvidx1, intvidx2) {
// base case
if (s1.length() == vidx1)
returns2.length() - vidx2;
if (s2.length() == vidx2) {
returns1.length() - vidx1;
}
charch1 = s1.charAt(vidx1);
charch2 = s2.charAt(vidx2);
intdistance = 0;
if (ch1 == ch2) {
distance = edRecursionVirtualIndex(s1, s2, vidx1 + 1, vidx2 + 1);
} else {
intinsertion = edRecursionVirtualIndex(s1, s2, vidx1 + 1, vidx2);
intdeletion = edRecursionVirtualIndex(s1, s2, vidx1, vidx2 + 1);
intreplacement = edRecursionVirtualIndex(s1, s2, vidx1 + 1, vidx2 + 1);
distance = 1 + Math.min(insertion, Math.min(deletion, replacement));
}
returndistance;
}
// O(mn) Time | O(mn) Space + recursion extra space
publicstaticinteditDistanceTopDownDP(Strings1, Strings2, intvidx1, intvidx2, int[][] storage) {
// base case
if (s1.length() == vidx1)
returns2.length() - vidx2;
if (s2.length() == vidx2) {
returns1.length() - vidx1;
}
if (storage[vidx1][vidx2] != -1) {
returnstorage[vidx1][vidx2];
}
charch1 = s1.charAt(vidx1);
charch2 = s2.charAt(vidx2);
intdistance = 0;
if (ch1 == ch2) {
distance = editDistanceTopDownDP(s1, s2, vidx1 + 1, vidx2 + 1, storage);
} else {
intinsertion = editDistanceTopDownDP(s1, s2, vidx1 + 1, vidx2, storage);
intdeletion = editDistanceTopDownDP(s1, s2, vidx1, vidx2 + 1, storage);
intreplacement = editDistanceTopDownDP(s1, s2, vidx1 + 1, vidx2 + 1, storage);
distance = 1 + Math.min(insertion, Math.min(deletion, replacement));
}
storage[vidx1][vidx2] = distance;
returndistance;
}
// O(mn) Time | O(mn) Space
publicstaticinteditDistanceBottomUpDP(Strings1, Strings2) {
int[][] storage = newint[s1.length() + 1][s2.length() + 1];
// filling: bottom to top, right to left
for (introw = s1.length(); row >= 0; row--) {
for (intcol = s2.length(); col >= 0; col--) {
// base cases
if (row == s1.length()) {
storage[row][col] = s2.length() - col;
} elseif (col == s2.length()) {
storage[row][col] = s1.length() - row;
} else {
if (s1.charAt(row) == s2.charAt(col)) {
storage[row][col] = storage[row + 1][col + 1];
} else {
intinsertionFactor = storage[row + 1][col];
intdeletionFactor = storage[row][col + 1];
intreplaceFactor = storage[row + 1][col + 1];
storage[row][col] = 1 + Math.min(insertionFactor, Math.min(deletionFactor, replaceFactor));
}
}
}
}
returnstorage[0][0];
}
}
