ZacharyZhang-NY
b7fca0146d
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54 lines
1.4 KiB
JavaScript
54 lines
1.4 KiB
JavaScript
// Myers' diff over two lists.
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/** Equal pairs between `a` and `b`, in order. */
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export function common(a, b, same) {
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const n = a.length
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const m = b.length
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const max = n + m
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const reach = new Map([[1, 0]])
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const trace = []
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for (let d = 0; d <= max; d++) {
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trace.push(new Map(reach))
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for (let k = -d; k <= d; k += 2) {
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const down = k === -d || (k !== d && reach.get(k - 1) < reach.get(k + 1))
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let x = down ? reach.get(k + 1) : reach.get(k - 1) + 1
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let y = x - k
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while (x < n && y < m && same(a[x], b[y])) {
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x += 1
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y += 1
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}
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reach.set(k, x)
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if (x >= n && y >= m) return walk(trace, n, m)
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}
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}
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throw new Error('diff did not end')
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}
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/** Back through the trace: each equal pair, in order. */
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function walk(trace, n, m) {
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const pairs = []
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let x = n
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let y = m
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for (let d = trace.length - 1; d > 0; d--) {
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const reach = trace[d]
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const k = x - y
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const down = k === -d || (k !== d && reach.get(k - 1) < reach.get(k + 1))
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const from = down ? k + 1 : k - 1
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const fromX = reach.get(from)
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const fromY = fromX - from
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while (x > fromX + (down ? 0 : 1) && y > fromY + (down ? 1 : 0)) {
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x -= 1
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y -= 1
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pairs.push([x, y])
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}
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x = fromX
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y = fromY
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}
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while (x > 0 && y > 0) {
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x -= 1
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y -= 1
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pairs.push([x, y])
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}
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return pairs.reverse()
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}
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