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Shuffle search substr
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| String::linear_search = (from,to,sub) -> | |
| i = from | |
| j = 0 | |
| max = sub.length | |
| while (to - i + 1) >= (max-j) | |
| if @[i] == sub[j] | |
| i++; j++ | |
| else | |
| j = 0; i++ | |
| return true if j == max | |
| return false | |
| # Algorithm description | |
| # Summary: Instead of linearly searching for your substring whether it exists | |
| # if we randomly search segments then it can have a better avg time | |
| # The main recipe for random search will be: | |
| # 1. Start with initial string as first segment | |
| # 2. Choose the middle letter of this segment | |
| # 3. If this letter exists in substring then | |
| # 3.1 Find the bounds around this letter in which you should do linear | |
| # search | |
| # 3.2 Either your substr is within these bounds and if not then simply | |
| # divide your segment into two by dividing on the segment you | |
| # searched on | |
| # 4. If this letter does not exist then simply divide into 2 segments | |
| # 5 If segment has enough length then push them into segment lists | |
| # 6. Got to step1 and randomly choose a segment | |
| String::shuffle_search = (sub) -> | |
| chars = {} | |
| _.each sub, (v, i, arr) -> | |
| chars[v] = {"first": i, "last": i} unless chars[v] | |
| chars[v]["last"] = i | |
| segments = [] | |
| segments.push {"begin": 0, "end": @length - 1} | |
| found = false | |
| max_len_sub = sub.length | |
| until segments.length == 0 || found | |
| randomSegment_i = Math.floor(Math.random() * segments.length) | |
| segment = segments.splice(randomSegment_i, 1)[0] | |
| continue if (segment["end"] - segment["begin"]) < max_len_sub | |
| #randomChar_i=Math.floor(Math.random() *segment["end"])+segment["begin"] | |
| randomChar_i = Math.floor((segment["end"] - segment["begin"]) / 2) | |
| randomChar_i += segment["begin"] | |
| c = @[randomChar_i] | |
| if chars[c] | |
| left_bound = randomChar_i - chars[c]["last"] | |
| right_bound = randomChar_i + max_len_sub - chars[c]["first"] | |
| virt_left_bound = if left_bound < segment["begin"] | |
| segment["begin"] | |
| else | |
| if chars[@[left_bound]] | |
| left_bound - chars[@[left_bound]]["last"] | |
| else | |
| left_bound | |
| virt_left_bound = segment["begin"] if segment["begin"] > virt_left_bound | |
| virt_right_bound = if right_bound > segment["end"] | |
| segment["end"] | |
| else | |
| if chars[@[right_bound]] | |
| right_bound + max_len_sub - chars[@[right_bound]]["first"] | |
| else | |
| right_bound | |
| virt_right_bound = segment["end"] if segment["end"] < virt_left_bound | |
| found = @linear_search virt_left_bound, virt_right_bound, sub | |
| break if found | |
| if left_bound - segment["begin"] >= max_len_sub | |
| segments.push {"begin": segment["begin"], "end": left_bound - 1} | |
| if segment["end"] - right_bound >= max_len_sub | |
| segments.push {"begin": right_bound + 1, "end": segment["end"]} | |
| else | |
| if randomChar_i - segment["begin"] >= max_len_sub | |
| segments.push {"begin": segment["begin"], "end": randomChar_i - 1} | |
| if segment["end"] - randomChar_i >= max_len_sub | |
| segments.push {"begin": randomChar_i + 1, "end": segment["end"]} | |
| return found |
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| describe "string shuffle search problem", -> | |
| it "does linear search properly", -> | |
| a = "1233456" | |
| b = "334" | |
| expect(a.linear_search 0, a.length-1, b).toBe(true) | |
| a = "abcdedfgdfhaLMMNbcd" | |
| b = "LMMN" | |
| expect(a.linear_search 0, a.length-1, b).toBe(true) | |
| it "detects presence", -> | |
| a = "abcdedfgdfhaLMMNbcd" | |
| b = "LMMN" | |
| expect(a.shuffle_search b).toBe(true) | |
| it "detects absence", -> | |
| a = "abcdedfgdhabcd" | |
| b = "LMMN" | |
| expect(a.shuffle_search b).toBe(false) | |
| it "compares better to linear search", -> | |
| [a,b] = ["",""] | |
| _.times 9000000*2, -> | |
| a += String.fromCharCode(Math.floor(Math.random()*25)+97) | |
| _.times 9800, -> | |
| b += String.fromCharCode(Math.floor(Math.random()*25)+65) | |
| a += b | |
| _.times 1000000*2, -> | |
| a += String.fromCharCode(Math.floor(Math.random()*25)+97) | |
| t1 = new Date() | |
| r1 = a.linear_search 0, a.length-1, b | |
| t2 = new Date() | |
| r2 = a.shuffle_search b | |
| t3 = new Date() | |
| expect(r1).toBe(true) | |
| expect(r2).toBe(true) | |
| console.log "\nTime taken linear- #{(t2 - t1)/1000}s shuffle- #{(t3 - t2)/1000}s" |
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