@marcusgao The calculation is from right to left, even though pos[p1] >= 10. it's still Ok, because current p1 will be p2 in next step, the % operation will always get right result in p2 position. finally, the overflow will end at head, but it will not overflow again. For example, 99 * 99 = 9801, 2 digit number multiplication, the result length will not exceed 4 digit.

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