Add 0873

Author: zangbianxuegu

0873. Length of Longest Fibonacci Subsequence.js

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+// A sequence X_1, X_2, ..., X_n is fibonacci - like if:
+
+// n >= 3
+// X_i + X_{ i + 1 } = X_{ i + 2 } for all i + 2 <= n
+// Given a strictly increasing array A of positive integers forming a sequence, find the length of the longest fibonacci - like subsequence of A.If one does not exist, return 0.
+
+// (Recall that a subsequence is derived from another sequence A by deleting any number of elements(including none) from A, 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 <= 1000
+// 1 <= 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++.)
+
+
+// Dynamic Programming
+/**
+ * @param {number[]} A
+ * @return {number}
+ */
+var lenLongestFibSubseq = function (A) {
+  let len = A.length
+  let map = {}
+  let res = 0
+  let dp = [...Array(len)].map(r => Array(len).fill(2))
+  for (let i = 0; i < len; i++) {
+    map[A[i]] = i
+    for (let j = 0; j < i; j++) {
+      if (A[i] - A[j] < A[j] && A[i] - A[j] in map) {
+        dp[j][i] = Math.max(dp[j][i], 1 + dp[map[A[i] - A[j]]][j])
+      }
+      res = Math.max(res, dp[j][i])
+    }
+  }
+  return res === 2 ? 0 : res
+}
+// Runtime: 204 ms, faster than 70.67 % of JavaScript online submissions for Length of Longest Fibonacci Subsequence.
+// Memory Usage: 82.1 MB, less than 50.00 % of JavaScript online submissions for Length of Longest Fibonacci Subsequence.