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Diffstat (limited to 'len_longest_fib_seq.c')
-rw-r--r-- | len_longest_fib_seq.c | 56 |
1 files changed, 56 insertions, 0 deletions
diff --git a/len_longest_fib_seq.c b/len_longest_fib_seq.c new file mode 100644 index 0000000..7223f2c --- /dev/null +++ b/len_longest_fib_seq.c @@ -0,0 +1,56 @@ +// 873. Length of Longest Fibonacci Subsequence +#include "leetcode.h" + +/* + * a sequence 'x1, x2, ..., xn' is fibonacci like if 'n >= 3' and 'x_i + x_i + 1 + * == x_i + 2' for all 'i + 2 <= n'. given a strictly increasing 'arr' of + * positive integers forming a sequence, return the length of the longest + * fibonacci like subsequence of 'arr'. if one does not exist, return 0. a + * subsequence is derived from another sequence 'arr' by deleting any number of + * elements (including none) from 'arr', without changing the order of the + * remaining elements. + */ + +static int a_max; + +int helper(int *arr, int *map, int i, int j, int sum) { + int cnt = 0; + while (sum <= a_max) { + if (!map[sum]) + break; + cnt++; + i = j; + j = map[sum] - 1; + sum = arr[i] + arr[j]; + } + return cnt; +} + +int lenLongestFibSubseq(int *arr, int arrSize) { + a_max = arr[arrSize - 1]; + int map_size = a_max + 1; + int *map = (int *)calloc(map_size, sizeof(int)); + int cnt = 0, i, j, sum, tmp; + for (int i = 0; i < arrSize; i++) + map[arr[i]] = i + 1; + for (int i = 0; i < arrSize; i++) { + for (int j = i + 1; j < arrSize; j++) { + sum = arr[i] + arr[j]; + if (sum > a_max) + break; + if (!map[sum]) + continue; + tmp = helper(arr, map, i, j, sum); + cnt = fmax(cnt, tmp); + } + } + cnt += 2; + free(map); + return cnt > 2 ? cnt : 0; +} + +int main() { + int a1[] = {1, 2, 3, 4, 5, 6, 7, 8}, a2[] = {1, 3, 7, 11, 12, 14, 18}; + printf("%d\n", lenLongestFibSubseq(a1, ARRAY_SIZE(a1))); // expect: 5 + printf("%d\n", lenLongestFibSubseq(a2, ARRAY_SIZE(a2))); // expect: 3 +} |