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Fix #156 #173

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Fix #156 #173

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69a833f
src/filters/lcs.js: implement backtrack in a iterative way
dirb Feb 20, 2017
efe3911
src/filters/lcs.js: optimize by trim off matching items at the beginn…
dirb Feb 26, 2017
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78 changes: 57 additions & 21 deletions src/filters/lcs.js
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,23 @@ var defaultMatch = function(array1, array2, index1, index2) {
};

var lengthMatrix = function(array1, array2, match, context) {
var len1 = array1.length;
var len2 = array2.length;
var start = 0;
var end1 = array1.length;
var end2 = array2.length;

//trim off the matching items at the beginning
while (start < end1 && start < end2 && match(array1, array2, start, start, context)) {
start++;
}

//trim off the matching items at the end
while (start < end1 && start < end2 && match(array1, array2, end1 - 1, end2 - 1, context)) {
end1--;
end2--;
}

var len1 = end1 - start;
var len2 = end2 - start;
var x, y;

// initialize empty matrix of len1+1 x len2+1
Expand All @@ -24,10 +39,13 @@ var lengthMatrix = function(array1, array2, match, context) {
}
}
matrix.match = match;
matrix.start = start;
matrix.end1 = end1;
matrix.end2 = end2;
// save sequence lengths for each coordinate
for (x = 1; x < len1 + 1; x++) {
for (y = 1; y < len2 + 1; y++) {
if (match(array1, array2, x - 1, y - 1, context)) {
if (match(array1, array2, start + x - 1, start + y - 1, context)) {
matrix[x][y] = matrix[x - 1][y - 1] + 1;
} else {
matrix[x][y] = Math.max(matrix[x - 1][y], matrix[x][y - 1]);
Expand All @@ -37,34 +55,52 @@ var lengthMatrix = function(array1, array2, match, context) {
return matrix;
};

var backtrack = function(matrix, array1, array2, index1, index2, context) {
if (index1 === 0 || index2 === 0) {
return {
sequence: [],
indices1: [],
indices2: []
};
var backtrack = function(matrix, array1, array2, context) {
var subsequence = {
sequence: [],
indices1: [],
indices2: []
};

var x;
//push matching items at the beginning
for (x = 0; x < matrix.start; x++) {
subsequence.sequence.push(array1[x]);
subsequence.indices1.push(x);
subsequence.indices2.push(x);
}

if (matrix.match(array1, array2, index1 - 1, index2 - 1, context)) {
var subsequence = backtrack(matrix, array1, array2, index1 - 1, index2 - 1, context);
subsequence.sequence.push(array1[index1 - 1]);
subsequence.indices1.push(index1 - 1);
subsequence.indices2.push(index2 - 1);
return subsequence;
//push matching items at the end
for (x = matrix.end1; x < array1.length; x++) {
subsequence.sequence.push(array1[x]);
subsequence.indices1.push(x);
subsequence.indices2.push(matrix.end2 + (x - matrix.end1));
}

if (matrix[index1][index2 - 1] > matrix[index1 - 1][index2]) {
return backtrack(matrix, array1, array2, index1, index2 - 1, context);
} else {
return backtrack(matrix, array1, array2, index1 - 1, index2, context);
var index1 = matrix.end1 - matrix.start;
var index2 = matrix.end2 - matrix.start;

while (0 < index1 && 0 < index2) {
if (matrix.match(array1, array2, matrix.start + index1 - 1, matrix.start + index2 - 1, context)) {
subsequence.sequence.push(array1[matrix.start + index1 - 1]);
subsequence.indices1.push(matrix.start + index1 - 1);
subsequence.indices2.push(matrix.start + index2 - 1);
index1--;
index2--;
} else if (matrix[index1][index2 - 1] > matrix[index1 - 1][index2]) {
index2--;
} else {
index1--;
}
}

return subsequence;
};

var get = function(array1, array2, match, context) {
context = context || {};
var matrix = lengthMatrix(array1, array2, match || defaultMatch, context);
var result = backtrack(matrix, array1, array2, array1.length, array2.length, context);
var result = backtrack(matrix, array1, array2, context);
if (typeof array1 === 'string' && typeof array2 === 'string') {
result.sequence = result.sequence.join('');
}
Expand Down