55 lines
1.1 KiB
Go
55 lines
1.1 KiB
Go
// Package patience implements the Patience Diff algorithm.
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package patience
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// LCS computes the longest common subsequence of two string
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// slices and returns the index pairs of the LCS.
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func LCS(a, b []string) [][2]int {
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// Initialize the LCS table.
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lcs := make([][]int, len(a)+1)
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for i := 0; i <= len(a); i++ {
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lcs[i] = make([]int, len(b)+1)
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}
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// Populate the LCS table.
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for i := 1; i < len(lcs); i++ {
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for j := 1; j < len(lcs[i]); j++ {
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if a[i-1] == b[j-1] {
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lcs[i][j] = lcs[i-1][j-1] + 1
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} else {
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lcs[i][j] = max(lcs[i-1][j], lcs[i][j-1])
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}
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}
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}
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// Backtrack to find the LCS.
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i, j := len(a), len(b)
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s := make([][2]int, 0, lcs[i][j])
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for i > 0 && j > 0 {
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switch {
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case a[i-1] == b[j-1]:
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s = append(s, [2]int{i - 1, j - 1})
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i--
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j--
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case lcs[i-1][j] > lcs[i][j-1]:
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i--
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default:
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j--
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}
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}
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// Reverse the backtracked LCS.
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for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
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s[i], s[j] = s[j], s[i]
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}
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return s
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}
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// max returns the maximum of two integers.
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func max(a, b int) int {
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if a > b {
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return a
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}
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return b
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}
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