372. Super Pow
Your task is to calculate ab mod 1337 where a is a positive integer and b is an extremely large positive integer given in the form of an array.
Example 1:
Input: a = 2, b = [3] Output: 8
Example 2:
Input: a = 2, b = [1,0] Output: 1024
Example 3:
Input: a = 1, b = [4,3,3,8,5,2] Output: 1
Example 4:
Input: a = 2147483647, b = [2,0,0] Output: 1198
Constraints:
1 <= a <= 231 - 11 <= b.length <= 20000 <= b[i] <= 9bdoesn't contain leading zeros.
Rust Solution
struct Solution;
impl Solution {
fn super_pow(a: i32, mut b: Vec<i32>) -> i32 {
let a = a % 1337;
if let Some(last) = b.pop() {
Self::pow_mod(Self::super_pow(a, b) % 1337, 10) * Self::pow_mod(a, last) % 1337
} else {
1
}
}
fn pow_mod(a: i32, k: i32) -> i32 {
let mut res = 1;
for _ in 0..k {
res *= a;
res %= 1337;
}
res
}
}
#[test]
fn test() {
let a = 2;
let b = vec![3];
let res = 8;
assert_eq!(Solution::super_pow(a, b), res);
let a = 2;
let b = vec![1, 0];
let res = 1024;
assert_eq!(Solution::super_pow(a, b), res);
}
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