标签：continue i+1 sequence NPU ... shm seq ini highlight
A sequence
X_1, X_2, ..., X_nis fibonacci-like if:
n >= 3X_i + X_{i+1} = X_{i+2}for alli + 2 <= nGiven a strictly increasing array
Aof positive integers forming a sequence, find the length of the longest fibonacci-like subsequence ofA. If one does not exist, return 0.(Recall that a subsequence is derived from another sequence
Aby deleting any number of elements (including none) fromA, without changing the order of the remaining elements. For example,[3, 5, 8]is a subsequence of[3, 4, 5, 6, 7, 8].)
Example 1:
Input: [1,2,3,4,5,6,7,8] Output: 5 Explanation: The longest subsequence that is fibonacci-like: [1,2,3,5,8].Example 2:
Input: [1,3,7,11,12,14,18] Output: 3 Explanation: The longest subsequence that is fibonacci-like: [1,11,12], [3,11,14] or [7,11,18].
Note:
3 <= A.length <= 10001 <= A[0] < A[1] < ... < A[A.length - 1] <= 10^9- (The time limit has been reduced by 50% for submissions in Java, C, and C++.)
Approach #1: unordered_map. [C++]
class Solution {
public:
int lenLongestFibSubseq(vector<int>& A) {
unordered_map<int, int> memo;
int len = A.size();
int ans = 0, temp = 0;
for (int i = 0; i < len; ++i)
memo[A[i]] = i;
for (int i = 0; i < len; ++i) {
for (int j = i + 1; j < len; ++j) {
int ant = 2;
int last_idx = i;
for (int cur_idx = j; cur_idx < len; ) {
temp = A[last_idx] + A[cur_idx];
if (memo.count(temp)) {
ant++;
last_idx = cur_idx;
cur_idx = memo[temp];
} else break;
}
ans = max(ans, ant);
}
}
return ans == 2 ? 0 : ans;
}
};
Approach #2: DP. [Java]
class Solution {
public int lenLongestFibSubseq(int[] A) {
int n = A.length;
int res = 0;
int[][] dp = new int[n+1][n+1];
for (int[] row : dp) Arrays.fill(row, 2);
Map<Integer, Integer> pos = new HashMap<>();
for (int i = 0; i < n; ++i) pos.put(A[i], i);
for (int j = 2; j < n; ++j) {
for (int i = j-1; i > 0; --i) {
int prev = A[j] - A[i];
if (prev >= A[i]) break;
if (!pos.containsKey(prev)) continue;
dp[i][j] = dp[pos.get(prev)][i] + 1;
res = Math.max(res, dp[i][j]);
}
}
return res;
}
}
Analysis:
873. Length of Longest Fibonacci Subsequence
标签：continue i+1 sequence NPU ... shm seq ini highlight
原文地址：https://www.cnblogs.com/ruruozhenhao/p/10583405.html
