Mercurial > hg
annotate mercurial/ancestor.py @ 17509:f7767f52e9eb
spelling: recursion
author | timeless@mozdev.org |
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date | Fri, 17 Aug 2012 13:58:18 -0700 |
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1 # ancestor.py - generic DAG ancestor algorithm for mercurial |
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2 # |
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3 # Copyright 2006 Matt Mackall <mpm@selenic.com> |
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4 # |
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5 # This software may be used and distributed according to the terms of the |
10263 | 6 # GNU General Public License version 2 or any later version. |
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7 |
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8 import heapq |
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9 |
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10 def ancestor(a, b, pfunc): |
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11 """ |
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12 Returns the common ancestor of a and b that is furthest from a |
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13 root (as measured by longest path) or None if no ancestor is |
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14 found. If there are multiple common ancestors at the same |
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15 distance, the first one found is returned. |
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16 |
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17 pfunc must return a list of parent vertices for a given vertex |
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18 """ |
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19 |
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20 if a == b: |
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21 return a |
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22 |
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23 a, b = sorted([a, b]) |
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24 |
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25 # find depth from root of all ancestors |
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26 # depth is stored as a negative for heapq |
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27 parentcache = {} |
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28 visit = [a, b] |
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29 depth = {} |
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30 while visit: |
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31 vertex = visit[-1] |
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32 pl = pfunc(vertex) |
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33 parentcache[vertex] = pl |
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34 if not pl: |
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35 depth[vertex] = 0 |
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36 visit.pop() |
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37 else: |
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38 for p in pl: |
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39 if p == a or p == b: # did we find a or b as a parent? |
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40 return p # we're done |
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41 if p not in depth: |
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42 visit.append(p) |
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43 if visit[-1] == vertex: |
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44 # -(maximum distance of parents + 1) |
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45 depth[vertex] = min([depth[p] for p in pl]) - 1 |
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46 visit.pop() |
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47 |
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48 # traverse ancestors in order of decreasing distance from root |
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49 def ancestors(vertex): |
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50 h = [(depth[vertex], vertex)] |
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51 seen = set() |
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52 while h: |
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53 d, n = heapq.heappop(h) |
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54 if n not in seen: |
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55 seen.add(n) |
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56 yield (d, n) |
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57 for p in parentcache[n]: |
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58 heapq.heappush(h, (depth[p], p)) |
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59 |
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60 def generations(vertex): |
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61 sg, s = None, set() |
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62 for g, v in ancestors(vertex): |
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63 if g != sg: |
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64 if sg: |
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65 yield sg, s |
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66 sg, s = g, set((v,)) |
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67 else: |
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68 s.add(v) |
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69 yield sg, s |
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70 |
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71 x = generations(a) |
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72 y = generations(b) |
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73 gx = x.next() |
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74 gy = y.next() |
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75 |
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76 # increment each ancestor list until it is closer to root than |
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77 # the other, or they match |
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78 try: |
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79 while True: |
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80 if gx[0] == gy[0]: |
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81 for v in gx[1]: |
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82 if v in gy[1]: |
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83 return v |
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84 gy = y.next() |
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85 gx = x.next() |
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86 elif gx[0] > gy[0]: |
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87 gy = y.next() |
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88 else: |
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89 gx = x.next() |
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90 except StopIteration: |
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91 return None |