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modular multiplicative inverse
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| def modinv(n, mod): | |
| t, w, r = 0, 1, mod | |
| while n: | |
| (q, n), r = divmod(r, n), n | |
| t, w = w, t - q * w | |
| if r > 1: raise Exception('not invertible ' + repr(n)) | |
| if t < 0: t += mod | |
| return t |
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Python 3.8:
pow(n, -1, mod)