rustdoc: collapse edit distance state into an object
This commit is contained in:
Michael Howell
parent
dfd9e5e3fa
commit
ce795d9ca8
@ -90,91 +90,97 @@ function printTab(nb) {
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* algorithm should not matter to the caller of the methods, which is why it is not noted in the
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* documentation.
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*/
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let editDistanceCurrent = [];
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let editDistancePrev = [];
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let editDistancePrevPrev = [];
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function editDistance(a, b, limit) {
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// Ensure that `b` is the shorter string, minimizing memory use.
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if (a.length < b.length) {
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const aTmp = a;
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a = b;
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b = aTmp;
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}
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const minDist = a.length - b.length;
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// If we know the limit will be exceeded, we can return early.
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if (minDist > limit) {
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return limit + 1;
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}
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// Strip common prefix.
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// We know that `b` is the shorter string, so we don't need to check
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// `a.length`.
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while (b.length > 0 && b[0] === a[0]) {
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a = a.substring(1);
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b = b.substring(1);
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}
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// Strip common suffix.
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while (b.length > 0 && b[b.length - 1] === a[a.length - 1]) {
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a = a.substring(0, a.length - 1);
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b = b.substring(0, b.length - 1);
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}
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// If either string is empty, the distance is the length of the other.
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// We know that `b` is the shorter string, so we don't need to check `a`.
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if (b.length === 0) {
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return minDist;
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}
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const aLength = a.length;
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const bLength = b.length;
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for (let i = 0; i <= bLength; ++i) {
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editDistanceCurrent[i] = 0;
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editDistancePrev[i] = i;
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editDistancePrevPrev[i] = Number.MAX_VALUE;
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}
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// row by row
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for (let i = 1; i <= aLength; ++i) {
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editDistanceCurrent[0] = i;
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const aIdx = i - 1;
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// column by column
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for (let j = 1; j <= bLength; ++j) {
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const bIdx = j - 1;
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// There is no cost to substitute a character with itself.
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const substitutionCost = a[aIdx] === b[bIdx] ? 0 : 1;
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editDistanceCurrent[j] = Math.min(
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// deletion
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editDistancePrev[j] + 1,
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// insertion
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editDistanceCurrent[j - 1] + 1,
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// substitution
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editDistancePrev[j - 1] + substitutionCost
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);
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if ((i > 1) && (j > 1) && (a[aIdx] === b[bIdx - 1]) && (a[aIdx - 1] === b[bIdx])) {
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// transposition
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editDistanceCurrent[j] = Math.min(
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editDistanceCurrent[j],
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editDistancePrevPrev[j - 2] + 1
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);
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}
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const editDistanceState = {
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current: [],
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prev: [],
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prevPrev: [],
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calculate: function calculate(a, b, limit) {
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// Ensure that `b` is the shorter string, minimizing memory use.
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if (a.length < b.length) {
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const aTmp = a;
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a = b;
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b = aTmp;
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}
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// Rotate the buffers, reusing the memory
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const prevPrevTmp = editDistancePrevPrev;
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editDistancePrevPrev = editDistancePrev;
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editDistancePrev = editDistanceCurrent;
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editDistanceCurrent = prevPrevTmp;
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}
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const minDist = a.length - b.length;
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// If we know the limit will be exceeded, we can return early.
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if (minDist > limit) {
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return limit + 1;
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}
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// `prev` because we already rotated the buffers.
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const distance = editDistancePrev[bLength];
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return distance <= limit ? distance : (limit + 1);
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// Strip common prefix.
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// We know that `b` is the shorter string, so we don't need to check
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// `a.length`.
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while (b.length > 0 && b[0] === a[0]) {
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a = a.substring(1);
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b = b.substring(1);
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}
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// Strip common suffix.
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while (b.length > 0 && b[b.length - 1] === a[a.length - 1]) {
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a = a.substring(0, a.length - 1);
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b = b.substring(0, b.length - 1);
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}
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// If either string is empty, the distance is the length of the other.
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// We know that `b` is the shorter string, so we don't need to check `a`.
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if (b.length === 0) {
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return minDist;
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}
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const aLength = a.length;
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const bLength = b.length;
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for (let i = 0; i <= bLength; ++i) {
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this.current[i] = 0;
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this.prev[i] = i;
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this.prevPrev[i] = Number.MAX_VALUE;
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}
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// row by row
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for (let i = 1; i <= aLength; ++i) {
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this.current[0] = i;
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const aIdx = i - 1;
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// column by column
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for (let j = 1; j <= bLength; ++j) {
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const bIdx = j - 1;
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// There is no cost to substitute a character with itself.
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const substitutionCost = a[aIdx] === b[bIdx] ? 0 : 1;
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this.current[j] = Math.min(
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// deletion
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this.prev[j] + 1,
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// insertion
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this.current[j - 1] + 1,
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// substitution
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this.prev[j - 1] + substitutionCost
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);
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if ((i > 1) && (j > 1) && (a[aIdx] === b[bIdx - 1]) && (a[aIdx - 1] === b[bIdx])) {
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// transposition
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this.current[j] = Math.min(
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this.current[j],
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this.prevPrev[j - 2] + 1
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);
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}
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}
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// Rotate the buffers, reusing the memory
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const prevPrevTmp = this.prevPrev;
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this.prevPrev = this.prev;
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this.prev = this.current;
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this.current = prevPrevTmp;
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}
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// `prev` because we already rotated the buffers.
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const distance = this.prev[bLength];
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return distance <= limit ? distance : (limit + 1);
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},
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};
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function editDistance(a, b, limit) {
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return editDistanceState.calculate(a, b, limit);
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}
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function initSearch(rawSearchIndex) {
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