80 lines
2.0 KiB
JavaScript
80 lines
2.0 KiB
JavaScript
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(function (exports) {
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'use strict';
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var kmp = (function () {
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function builtKMPTable(str) {
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var res = [];
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var len;
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var front;
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var end;
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var found;
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for (var i = 1; i <= str.length; i += 1) {
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front = Math.max(1, i - ((res[i - 2] || 0) + 1));
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end = Math.min(i - 1, (res[i - 2] || 0) + 1);
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found = false;
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len = 0;
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while (end >= 1 && front <= i && !found) {
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if (str.substring(0, end) === str.substring(front, i)) {
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found = true;
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len = end;
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} else {
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end -= 1;
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front += 1;
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}
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}
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res[i - 1] = len;
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}
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return res;
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}
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/**
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* Knuth–Morris–Pratt algorithm. Searches for the position of
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* the first occurrence of a specified value in a string.
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*
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* @example
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*
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* var indexOf = require('path-to-algorithm/src/searching/'+
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* 'knuth-morris-pratt').kmp;
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* console.log(indexOf('hello', 'll')); // 2
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*
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* @public
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* @module searching/knuth-morris-pratt
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* @param {String} str String.
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* @param {String} substr Substring.
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* @return {Number} A Number, representing the position
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* where the specified substring occurs for the first
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* time, or -1 if it never occurs.
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*/
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function indexOf(str, substr) {
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if (str === substr) {
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return 0;
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}
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var table = builtKMPTable(substr);
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var i = 0;
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var j = 0;
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while (i < str.length) {
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if (str[i] === substr[j]) {
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i += 1;
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j += 1;
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}
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if (j === substr.length) {
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return i - j;
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}
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if (i < str.length && str[i] !== substr[j]) {
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if (j > 0 && table[j - 1] !== 0) {
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j = table[j - 1];
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} else {
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i += 1;
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j = 0;
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}
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}
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}
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return -1;
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}
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return indexOf;
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}());
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exports.kmp = kmp;
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})(typeof window === 'undefined' ? module.exports : window);
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