		@@ -0,0 +1,12 @@
	1	+---
	2	+issue: 1
	3	+status: working
	4	+tags: search
	5	+---
	6	+# two-opt
	7	+
	8	+Nearest neighbour, then 2-opt until no exchange of two edges shortens the tour.
	9	+
	10	+## Next
	11	+
	12	+Move short runs of cities too (Or-opt).

+28 −0 routes/two-opt/solve.py 新增查看文件

		@@ -0,0 +1,28 @@
	1	+"""Nearest neighbour, then 2-opt until no exchange of two edges shortens the tour."""
	2	+import json
	3	+import math
	4	+import sys
	5	+
	6	+p = json.load(sys.stdin)
	7	+n = len(p)
	8	+
	9	+
	10	+def d(i, j):
	11	+ return math.dist(p[i], p[j])
	12	+
	13	+
	14	+left, tour = set(range(1, n)), [0]
	15	+while left:
	16	+ nxt = min(left, key=lambda j: d(tour[-1], j))
	17	+ left.remove(nxt)
	18	+ tour.append(nxt)
	19	+better = True
	20	+while better:
	21	+ better = False
	22	+ for i in range(1, n - 1):
	23	+ for j in range(i + 1, n):
	24	+ a, b, c, e = tour[i - 1], tour[i], tour[j], tour[(j + 1) % n]
	25	+ if d(a, c) + d(b, e) < d(a, b) + d(c, e) - 1e-12:
	26	+ tour[i:j + 1] = reversed(tour[i:j + 1])
	27	+ better = True
	28	+print(json.dumps(tour))