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PrimeSubtractionOperation.java
59 lines (51 loc) · 1.4 KB
/
PrimeSubtractionOperation.java
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// https://leetcode.com/problems/prime-subtraction-operation
class Solution {
public boolean primeSubOperation(int[] nums) {
int max = 0;
boolean isIncreasing = true;
for (int i = 0; i < nums.length; i++) {
max = Math.max(max, nums[i]);
if (i > 0) {
isIncreasing &= nums[i] > nums[i - 1];
}
}
if (isIncreasing) {
return true;
}
int last = 0;
List<Integer> primes = primesUntil(max);
for (int x: nums) {
int ix = Collections.binarySearch(primes, x - last);
if (ix < 0) {
ix = -ix - 1;
}
ix -= 1;
if (ix < 0) {
if (x > last) {
last = x;
continue;
} else {
return false;
}
}
last = x - primes.get(ix);
}
return true;
}
List<Integer> primesUntil(int n) {
List<Integer> res = new ArrayList<>();
for (int i = 2; i <= n; i++) {
boolean isPrime = true;
for (int j = 2; j * j <= i; j++) {
if (i % j == 0) {
isPrime = false;
break;
}
}
if (isPrime) {
res.add(i);
}
}
return res;
}
}