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levenshtein distance; edit distance; 编辑距离
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/* | |
e.g. | |
levenshteinDistance("aa","a") = 1; | |
levenshteinDistance("ab","ab") = 1; | |
levenshteinDistance("a","b") = 1; | |
*/ | |
var levenshteinDistance = function(s, t) { | |
var d = []; //2d matrix | |
// Step 1 | |
var n = s.length; | |
var m = t.length; | |
if (n == 0) return m; | |
if (m == 0) return n; | |
//Create an array of arrays in javascript (a descending loop is quicker) | |
for (var i = n; i >= 0; i--) d[i] = []; | |
// Step 2 | |
for (var i = n; i >= 0; i--) d[i][0] = i; | |
for (var j = m; j >= 0; j--) d[0][j] = j; | |
// Step 3 | |
for (var i = 1; i <= n; i++) { | |
var s_i = s.charAt(i - 1); | |
// Step 4 | |
for (var j = 1; j <= m; j++) { | |
//Check the jagged ld total so far | |
if (i == j && d[i][j] > 4) return n; | |
var t_j = t.charAt(j - 1); | |
var cost = (s_i == t_j) ? 0 : 1; // Step 5 | |
//Calculate the minimum | |
var mi = d[i - 1][j] + 1; | |
var b = d[i][j - 1] + 1; | |
var c = d[i - 1][j - 1] + cost; | |
if (b < mi) mi = b; | |
if (c < mi) mi = c; | |
d[i][j] = mi; // Step 6 | |
//Damerau transposition | |
if (i > 1 && j > 1 && s_i == t.charAt(j - 2) && s.charAt(i - 2) == t_j) { | |
d[i][j] = Math.min(d[i][j], d[i - 2][j - 2] + cost); | |
} | |
} | |
} | |
// Step 7 | |
return d[n][m]; | |
} |
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