Created
May 14, 2011 18:03
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Rabin Karp in JS
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//RABIN KARP | |
var BASE = 256, | |
PRIME = 256199087; | |
function tonum(c){ | |
return c.charCodeAt(0); | |
} | |
function mod(a, p, m){ | |
if (p == 0) return 1; | |
var sqr = mod(a, p/2, m) % m; | |
sqr = (sqr * sqr) % m; | |
if (p & 1) return ((a % m) * sqr) % m; | |
else return sqr; | |
} | |
function rabinHash(P){ | |
var p = 0, m = P.length, | |
i, | |
q = PRIME, d = BASE; | |
for (i=0; i < m; i++) | |
{ | |
p = (d*p + tonum(P[i])) % q; | |
} | |
return p; | |
} | |
exports.rabinHash = rabinHash; | |
function rabinMatch(T, P){ | |
var i,j,p,t,n,m,h,found, | |
d = BASE, q = PRIME; | |
n = T.length - 1; | |
m = P.length - 1; | |
h = mod(d,m - 1,q); | |
p = t = 0; | |
for (i=0; i<m; i++) | |
{ | |
p = (d*p + tonum(P[i])) % q; | |
t = (d*t + tonum(T[i])) % q; | |
} | |
for (i=0; i<=n-m; i++) | |
{ | |
if (p == t) | |
{ | |
found = 1; | |
for (j=0; j<m; j++) | |
if (P[j] != T[i+j]) | |
{ | |
found = 0; | |
break; | |
} | |
if (found) return i; | |
} else { | |
t = (d*(t - ((tonum(T[i])*h) % q)) + | |
tonum(T[i+m])) % q; | |
} | |
} | |
return -1; | |
} |
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