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Java Solution for LeetCode algorithm problems, continually updating
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package g0501_0600.s0526_beautiful_arrangement;
// #Medium #Array #Dynamic_Programming #Bit_Manipulation #Backtracking #Bitmask
// #2022_07_28_Time_3_ms_(98.66%)_Space_41.5_MB_(24.19%)
public class Solution {
public int countArrangement(int n) {
return backtrack(n, n, new Integer[1 << (n + 1)], 0);
}
private int backtrack(int n, int index, Integer[] cache, int cacheindex) {
if (index == 0) {
return 1;
}
int result = 0;
if (cache[cacheindex] != null) {
return cache[cacheindex];
}
for (int i = n; i > 0; i--) {
if ((cacheindex & (1 << i)) == 0 && (i % (index) == 0 || (index) % i == 0)) {
result += backtrack(n, index - 1, cache, cacheindex | 1 << i);
}
}
cache[cacheindex] = result;
return result;
}
}