{"id":479,"date":"2013-09-19T17:14:26","date_gmt":"2013-09-19T09:14:26","guid":{"rendered":"http:\/\/coderbee.net\/?p=479"},"modified":"2013-09-20T09:29:22","modified_gmt":"2013-09-20T01:29:22","slug":"%e6%95%a3%e5%88%97","status":"publish","type":"post","link":"https:\/\/coderbee.net\/index.php\/algorithm\/20130919\/479","title":{"rendered":"\u6563\u5217"},"content":{"rendered":"<p>\u6563\u5217\u4e00\u822c\u4e5f\u53eb\u54c8\u5e0c\u3002\u6563\u5217\u8868\u4e5f\u53eb\u54c8\u5e0c\u8868\u3002\u672c\u4f4d\u5c06\u4ecb\u7ecd\u6563\u5217\u8868\u7684\u57fa\u672c\u77e5\u8bc6\u3001\u4e00\u81f4\u6027\u54c8\u5e0c\u3001\u54c8\u5e0c\u78b0\u649e\u653b\u51fb\u53caJava\u91cc\u7684\u54c8\u5e0c\u5b9e\u73b0\u3002<\/p>\n<h2>\u4ecb\u7ecd<\/h2>\n<p>\u6563\u5217\u8868\u662f\u666e\u901a\u6570\u7ec4\u6982\u5ff5\u7684\u63a8\u5e7f\uff0c\u5728\u6700\u574f\u60c5\u51b5\u4e0b\u67e5\u627e\u4e00\u4e2a\u5143\u7d20\u9700\u8981O(n)\uff0c\u5728\u4e00\u4e9b\u5408\u7406\u5047\u8bbe\u4e0b\uff0c\u67e5\u627e\u4e00\u4e2a\u5143\u7d20\u7684\u671f\u671b\u65f6\u95f4\u4e3aO(1)\u3002<\/p>\n<p>\u5728\u6563\u5217\u8868\u4e2d\uff0c\u4e0d\u662f\u76f4\u63a5\u628a\u5173\u952e\u5b57\u7528\u4f5c\u6570\u7ec4\u4e0b\u6807\uff0c\u800c\u662f\u6839\u636e\u5173\u952e\u5b57\u8ba1\u7b97\u51fa\u4e0b\u6807\u3002<\/p>\n<p>\u6563\u5217\u51fd\u6570\uff1a\u4f5c\u7528\u5c31\u662f\u6839\u636e\u5173\u952e\u5b57\u8ba1\u7b97\u51fa\u6570\u7ec4\u4e0b\u6807\u3002<\/p>\n<p>\u78b0\u649e\uff08collision\uff09\uff1a\u591a\u4e2a\u5173\u952e\u5b57\u6620\u5c04\u5230\u540c\u4e00\u4e2a\u6570\u7ec4\u4e0b\u6807\u4f4d\u7f6e\u3002<\/p>\n<p>\u69fd\uff1a\u4e00\u822c\u628a\u6563\u5217\u8868\u7684\u6570\u7ec4\u7684\u4e00\u4e2a\u5b58\u50a8\u5355\u5143\uff08\u5143\u7d20\uff09\u53eb\u505a\u69fd\u3002<\/p>\n<p>\u7b80\u5355\u4e00\u81f4\u6027\u6563\u5217\uff1a\uff08Simple uniform hashing\uff09\u5047\u8bbe\u4efb\u4f55\u5143\u7d20\u6563\u5217\u5230m\u4e2a\u69fd\u4e2d\u7684\u6bcf\u4e00\u4e2a\u7684\u53ef\u80fd\u6027\u662f\u76f8\u540c\u7684\uff0c\u4e14\u4e0e\u5176\u4ed6\u5143\u7d20\u5df2\u88ab\u6563\u5217\u5230\u4ec0\u4e48\u4f4d\u7f6e\u4e0a\u72ec\u7acb\u65e0\u5173\uff0c\u8fd9\u4e2a\u5047\u8bbe\u79f0\u4e3a\u7b80\u5355\u4e00\u81f4\u6027\u6563\u5217\u3002<\/p>\n<p><!--more--><\/p>\n<h2>\u76f4\u63a5\u5bfb\u5740\u8868<\/h2>\n<p>\u5f53\u5173\u952e\u5b57\u7684\u96c6\u5408\u8f83\u5c0f\u65f6\uff0c\u76f4\u63a5\u628a\u5bf9\u8c61\u653e\u5728\u8868\u7684\u69fd\u4e2d\uff0c\u8282\u7701\u7a7a\u95f4\uff1b\u901a\u5e38\u4e0d\u9700\u8981\u5b58\u50a8\u5bf9\u8c61\u7684\u5173\u952e\u5b57\u57df\uff0c\u56e0\u4e3a\u5982\u679c\u6709\u4e86\u4e00\u4e2a\u5bf9\u8c61\u5728\u8868\u4e2d\u7684\u4e0b\u6807\uff0c\u5c31\u53ef\u4ee5\u5f97\u5230\u5b83\u7684\u5173\u952e\u5b57\u3002\u7531\u4e8e\u6ca1\u6709\u5b58\u50a8\u5173\u952e\u5b57\uff0c\u5c31\u5fc5\u987b\u6709\u67d0\u79cd\u65b9\u6cd5\u6765\u786e\u5b9a\u67d0\u4e2a\u69fd\u662f\u5426\u4e3a\u7a7a\u3002<\/p>\n<p>\u5728\u76f4\u63a5\u5bfb\u5740\u7684\u65b9\u5f0f\u4e0b\uff0c\u5177\u6709\u5173\u952e\u5b57k\u7684\u5143\u7d20\u88ab\u5b58\u653e\u5728\u69fdk\u4e2d\u3002<\/p>\n<h2>\u6563\u5217\u8868<\/h2>\n<p>\u5728\u6563\u5217\u8868\u4e2d\uff0c\u5177\u6709\u5173\u952e\u5b57k\u7684\u5143\u7d20\u5b58\u653eh(k)\u4e2d\uff0c\u4e5f\u5c31\u662f\u901a\u8fc7\u6563\u5217\u51fd\u6570h\u6765\u786e\u5b9a\u5b58\u50a8\u7684\u69fd\u4f4d\u3002<\/p>\n<p>\u4f7f\u7528\u6563\u5217\u51fd\u6570\u7684\u95ee\u9898\u662f\u4e24\u4e2a\u5173\u952e\u5b57\u53ef\u80fd\u6620\u5c04\u5230\u540c\u4e00\u4e2a\u69fd\u4e0a\uff0c\u4e5f\u5c31\u662f\u53d1\u751f\u78b0\u649e\u3002\u901a\u8fc7\u7cbe\u5fc3\u8bbe\u8ba1\u7684\u968f\u673a\u6563\u5217\u51fd\u6570\u53ef\u4ee5\u5c3d\u91cf\u51cf\u5c11\u78b0\u649e\u3002<a href=\"\/\/coderbee.net\/wp-content\/uploads\/2013\/09\/hash_collision_chaining.jpg\"><img loading=\"lazy\" decoding=\"async\" src=\"\/\/coderbee.net\/wp-content\/uploads\/2013\/09\/hash_collision_chaining-300x133.jpg\" alt=\"hash_collision_chaining\" width=\"300\" height=\"133\" class=\"alignnone size-medium wp-image-478\" srcset=\"https:\/\/coderbee.net\/wp-content\/uploads\/2013\/09\/hash_collision_chaining-300x133.jpg 300w, https:\/\/coderbee.net\/wp-content\/uploads\/2013\/09\/hash_collision_chaining-1024x454.jpg 1024w, https:\/\/coderbee.net\/wp-content\/uploads\/2013\/09\/hash_collision_chaining-624x276.jpg 624w, https:\/\/coderbee.net\/wp-content\/uploads\/2013\/09\/hash_collision_chaining.jpg 1082w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><\/p>\n<h3>\u901a\u8fc7\u94fe\u63a5\u6cd5\u89e3\u51b3\u78b0\u649e<\/h3>\n<p>\u5728\u94fe\u63a5\u6cd5\uff08chaning\uff09\u4e2d\uff0c\u628a\u6563\u5217\u5230\u540c\u4e00\u69fd\u4e2d\u7684\u6240\u6709\u5143\u7d20\u90fd\u653e\u5728\u4e00\u4e2a\u94fe\u8868\u4e2d\u3002<\/p>\n<p>\u4ece\u56fe\u53ef\u77e5\uff0c\u63d2\u5165\u548c\u641c\u7d22\u7684\u65f6\u95f4\u4e0e\u94fe\u8868\u7684\u957f\u5ea6\u6210\u6b63\u6bd4\u3002<\/p>\n<p>\u67e5\u627e\u65f6\uff0c\u9996\u5148\u8981\u8ba1\u7b97\u51fa\u5173\u952e\u5b57\u5bf9\u5e94\u7684\u69fd\uff0c\u7136\u540e\u904d\u5386\u94fe\u8868\u5339\u914d\u5143\u7d20\u3002<\/p>\n<h2>\u6563\u5217\u51fd\u6570<\/h2>\n<p>\u4e00\u4e2a\u597d\u7684\u6563\u5217\u51fd\u6570\u5e94\uff08\u8fd1\u4f3c\u5730\uff09\u6ee1\u8db3\u7b80\u5355\u4e00\u81f4\u6027\u6563\u5217\u7684\u5047\u8bbe\u3002\u4e00\u79cd\u597d\u7684\u505a\u6cd5\u662f\u4ee5\u72ec\u7acb\u4e8e\u6570\u636e\u4e2d\u53ef\u80fd\u5b58\u5728\u7684\u4efb\u4f55\u6a21\u5f0f\u7684\u65b9\u5f0f\u5bfc\u51fa\u6563\u5217\u503c\u3002<\/p>\n<h3>\u9664\u6cd5\u6563\u5217\u6cd5<\/h3>\n<p>\u901a\u8fc7\u53d6\u5173\u952e\u5b57k\u9664\u4ee5m\u7684\u4f59\u6570\uff0c\u6765\u5c06\u5173\u952e\u5b57k\u6620\u5c04\u5230m\u4e2a\u69fd\u7684\u67d0\u4e00\u4e2a\u53bb\u3002\u6563\u5217\u51fd\u6570\u4e3a\uff1a<code>h(k) = k mod  m<\/code>\u3002m\u4e00\u822c\u53d6\u4e0e2\u7684\u6574\u6570\u5e42\u4e0d\u592a\u63a5\u8fd1\u7684\u8d28\u6570\u3002<\/p>\n<h3>\u4e58\u6cd5\u6563\u5217\u6cd5<\/h3>\n<p>\u7528\u5173\u952e\u5b57k\u4e58\u4e0a\u5e38\u6570A\uff080&lt;A&lt;1\uff09\uff0c\u5e76\u62bd\u53d6\u51fakA\u7684\u5c0f\u6570\u90e8\u5206\uff0c\u7528m\u4e58\u4ee5\u8fd9\u4e2a\u503c\uff0c\u518d\u53d6\u7ed3\u679c\u7684\u5e95(floor)\u3002\u6563\u5217\u51fd\u6570\u4e3a\uff1a <code>h(k) = floor(m * (k*A mod 1))<\/code>\u3002<\/p>\n<h3>\u5168\u57df\u6563\u5217<\/h3>\n<p>universal  hashing\uff1a\u968f\u673a\u5730\u9009\u62e9\u6563\u5217\u51fd\u6570\uff0c\u4f7f\u4e4b\u72ec\u7acb\u4e8e\u8981\u5b58\u50a8\u7684\u5173\u952e\u5b57\u3002<\/p>\n<p>\u5168\u57df\u6563\u5217\u7684\u57fa\u672c\u601d\u60f3\u662f\u5728\u6267\u884c\u5f00\u59cb\u65f6\uff0c\u5c31\u4ece\u4e00\u65cf\u4ed4\u7ec6\u8bbe\u8ba1\u7684\u51fd\u6570\u4e2d\uff0c\u968f\u673a\u5730\u9009\u62e9\u4e00\u4e2a\u4f5c\u4e3a\u6563\u5217\u51fd\u6570\u3002<\/p>\n<h2>\u5f00\u653e\u5bfb\u5740\u6cd5<\/h2>\n<p>\u5728\u5f00\u653e\u5bfb\u5740\u6cd5\uff08open addressing\uff09\u4e2d\uff0c\u6240\u6709\u7684\u5143\u7d20\u90fd\u5b58\u653e\u5728\u6563\u5217\u8868\u91cc\u3002\u5373\u6bcf\u4e2a\u8868\u9879\u6216\u5305\u542b\u52a8\u6001\u96c6\u5408\u7684\u4e00\u4e2a\u5143\u7d20\uff0c\u6216\u5305\u542bNIL\u3002\u5f53\u67e5\u627e\u4e00\u4e2a\u5143\u7d20\u65f6\uff0c\u8981\u68c0\u67e5\u6240\u6709\u7684\u8868\u9879\uff0c\u76f4\u5230\u627e\u5230\u6240\u9700\u7684\u5143\u7d20\u6216\u8005\u6700\u7ec8\u53d1\u73b0\u5143\u7d20\u4e0d\u5728\u8868\u4e2d\u3002<\/p>\n<p>\u4e0d\u50cf\u5728\u94fe\u63a5\u6cd5\u4e2d\uff0c\u8fd9\u91cc\u6ca1\u6709\u94fe\u8868\uff0c\u4e5f\u6ca1\u6709\u5143\u7d20\u5b58\u653e\u5728\u6563\u5217\u8868\u5916\u3002<\/p>\n<p>\u5728\u5f00\u653e\u5bfb\u5740\u6cd5\u4e2d\uff0c\u5f53\u8981\u63d2\u5165\u4e00\u4e2a\u5143\u7d20\u65f6\uff0c\u53ef\u4ee5\u8fde\u7eed\u5730\u68c0\u67e5\uff08\u6216\u79f0\u63a2\u67e5\uff09\u6563\u5217\u8868\u7684\u5404\u9879\uff0c\u76f4\u5230\u627e\u5230\u4e00\u4e2a\u7a7a\u69fd\u6765\u9632\u6b62\u5f85\u63d2\u5165\u7684\u5173\u952e\u5b57\u4e3a\u6b62\u3002\u5982\u679c\u9700\u8981\uff0c\u4f1a\u68c0\u67e5\u6240\u6709\u7684\u69fd\u3002<\/p>\n<p>\u63a2\u67e5\u65b9\u6cd5\u4e00\u822c\u6709\u4e09\u79cd\uff1a\u7ebf\u6027\u63a2\u67e5\u3001\u4e8c\u6b21\u63a2\u67e5\u3001\u53cc\u91cd\u63a2\u67e5\u3002<\/p>\n<h2>\u4e00\u81f4\u6027\u54c8\u5e0c<\/h2>\n<p>\u5047\u5982\u6709N\u53f0cache \u670d\u52a1\u5668\uff08\u7b80\u79f0 cache\uff09\uff0c\u90a3\u4e48\u5982\u4f55\u5c06\u4e00\u4e2a\u5bf9\u8c61object\u6620\u5c04\u5230N\u4e2acache\u4e0a\u5462\uff1f\u5f88\u53ef\u80fd\u4f1a\u91c7\u7528\u7c7b\u4f3c\u4e0b\u9762\u7684\u901a\u7528\u65b9\u6cd5\u8ba1\u7b97object\u7684hash\u503c\uff0c\u7136\u540e\u5747\u5300\u7684\u6620\u5c04\u5230\u5230N\u4e2acache \uff1b<code>hash(object)%N<\/code>\u3002<\/p>\n<p>\u8fd9\u6837\u7684\u8bdd\uff0c\u5982\u679c\u6709\u4e00\u53f0cache\u5f53\u673a\uff0c\u6620\u5c04\u5173\u7cfb\u53d8\u4e3a\uff1a<code>hash(object)%(N-1)<\/code>\uff1b\u65b0\u589e\u4e00\u53f0cache\u65f6\uff0c\u6620\u5c04\u5173\u7cfb\u53d8\u4e3a\uff1a<code>hash(object)%(N+1)<\/code>\u3002\u8fd9\u4e24\u79cd\u60c5\u51b5\u90fd\u4f1a\u5bfc\u81f4\u5bf9\u8c61\u88ab\u6620\u5c04\u5230\u4e0d\u540c\u7684\u7f13\u5b58\uff0c\u4ece\u800c\u5bfc\u81f4\u7f13\u5b58\u5931\u6548\u3002\u4e00\u81f4\u6027\u54c8\u5e0c\u5c31\u662f\u89e3\u51b3\u8fd9\u7c7b\u573a\u666f\u7684\u3002<\/p>\n<h3>\u5355\u8c03\u6027<\/h3>\n<p>\u5355\u8c03\u6027\uff08 Monotonicity \uff09\uff1a\u662f\u6307\u5982\u679c\u5df2\u7ecf\u6709\u4e00\u4e9b\u5185\u5bb9\u901a\u8fc7\u54c8\u5e0c\u6620\u5c04\u5230\u76f8\u5e94\u7684\u7f13\u51b2\u4e2d\uff0c\u53c8\u6709\u65b0\u7684\u7f13\u51b2\u52a0\u5165\u5230\u7cfb\u7edf\u4e2d\u3002\u54c8\u5e0c\u7684\u7ed3\u679c\u5e94\u80fd\u591f\u4fdd\u8bc1\u539f\u6709\u5df2\u5206\u914d\u7684\u5185\u5bb9\u53ef\u4ee5\u88ab\u6620\u5c04\u5230\u65b0\u7684\u7f13\u51b2\u4e2d\u53bb\uff0c\u800c\u4e0d\u4f1a\u88ab\u6620\u5c04\u5230\u65e7\u7684\u7f13\u51b2\u96c6\u5408\u4e2d\u7684\u5176\u4ed6\u7f13\u51b2\u533a\u3002<\/p>\n<p>consistent hashing \u662f\u4e00\u79cd hash \u7b97\u6cd5\uff0c\u7b80\u5355\u7684\u8bf4\uff0c\u5728\u79fb\u9664 \/ \u6dfb\u52a0\u4e00\u4e2a cache \u65f6\uff0c\u5b83\u80fd\u591f\u5c3d\u53ef\u80fd\u5c0f\u7684\u6539\u53d8\u5df2\u5b58\u5728 key \u6620\u5c04\u5173\u7cfb\uff0c\u5c3d\u53ef\u80fd\u7684\u6ee1\u8db3\u5355\u8c03\u6027\u7684\u8981\u6c42\u3002<\/p>\n<p>\u5047\u8bbe\u6709\u4e00\u4e2a\u54c8\u5e0c\u7a7a\u95f4\uff0c\u4e00\u81f4\u6027\u54c8\u5e0c\u9700\u8981\u628a\u5bf9\u8c61\u548ccache\u6620\u5c04\u5230\u8fd9\u4e2a\u7f13\u5b58\u7a7a\u95f4\u53bb\u3002<br \/>\n<a href=\"\/\/coderbee.net\/wp-content\/uploads\/2013\/09\/consistent_hashing.png\"><img loading=\"lazy\" decoding=\"async\" src=\"\/\/coderbee.net\/wp-content\/uploads\/2013\/09\/consistent_hashing.png\" alt=\"consistent_hashing\" width=\"283\" height=\"253\" class=\"alignnone size-full wp-image-481\" \/><\/a><br \/>\n\u5706\u5708\u8868\u793a\u54c8\u5e0c\u7a7a\u95f4\uff0c\u662f\u56fa\u5b9a\u7684\uff0c\u72ec\u7acb\u4e8ecache \u548c \u5bf9\u8c61\uff1b\u84dd\u8272\u7684\u7ed3\u70b9\u8868\u793acache\uff1b\u7ea2\u8272\u7684\u7ed3\u70b9\u8868\u793a\u5bf9\u8c61\u3002<\/p>\n<p>\u4e00\u81f4\u6027\u54c8\u5e0c\u7b97\u6cd5\u7684\u5de7\u5999\u4e4b\u5904\u5728\u4e8e\uff1a\u5bf9\u4e8e\u4e00\u4e2a\u5bf9\u8c61object\uff0c\u901a\u8fc7\u7ed9\u5b9a\u7684\u54c8\u5e0c\u7b97\u6cd5\u5f97\u5230\u5b83\u7684\u7684\u54c8\u5e0c\u503chashCode\uff0c\u8fd9\u4e2ahashCode\u5bf9\u5e94\u5728\u54c8\u5e0c\u7a7a\u95f4\u7684\u4e00\u4e2a\u70b9\uff0c\u4f46\u8fd9\u4e2ahashCode\u4e0d\u76f4\u63a5\u5bf9\u5e94\u4e00\u4e2acache\uff1b\u4e3a\u4e86\u627e\u5230\u8fd9\u4e2ahashCode\u5bf9\u5e94\u7684cache\uff0c\u9700\u8981\u6309\u4e00\u79cd\u56fa\u5b9a\u7684\u987a\u5e8f\uff08\u6bd4\u5982\u987a\u65f6\u9488\uff09\u5728\u54c8\u5e0c\u7a7a\u95f4\u4e0a\u67e5\u627e\u5b83cache\uff0c\u67e5\u627e\u5230\u7684\u7b2c\u4e00\u4e2acache\u5373\u4e3a\u8fd9\u4e2a\u5bf9\u8c61\u6240\u5bf9\u5e94\u7684cache\u3002\u76f8\u5f53\u4e8e\u4e8c\u6b21\u6563\u5217\u3002<\/p>\n<p>\u8981\u6ce8\u610f\u7684\u662f\uff1a\u901a\u8fc7hashCode\u5728\u54c8\u5e0c\u7a7a\u95f4\u67e5\u627ecache\u65f6\uff0c\u627e\u5230\u7684\u7b2c\u4e00\u4e2acache\u5c31\u662f\u5bf9\u8c61\u6240\u5bf9\u5e94\u7684cache\uff0c\u4e0d\u4f1a\u67e5\u627e\u540e\u7eed\u7684cache\uff0c\u8fd9\u5c31\u786e\u4fdd\u4e86\u4e00\u81f4\u6027\u54c8\u5e0c\u7b97\u6cd5\u5177\u6709\u8bbf\u95ee\u5c40\u90e8\u6027\u7684\u7279\u6027\u3002<\/p>\n<p>\u5047\u5982\u54c8\u5e0c\u7a7a\u95f4\u4e0a\u7684\u67e5\u627e\u987a\u5e8f\u4e3a\u987a\u65f6\u9488\u7684\uff1a<\/p>\n<ul>\n<li>\u5f53\u65b0\u589e\u4e00\u4e2acache D\u65f6\uff0c\u5b83\u6620\u5c04\u5230key2\u548ckey3\u4e4b\u95f4\uff0c\u90a3\u4e48\u53d7\u5f71\u54cd\u7684\u5bf9\u8c61\u53ea\u5c40\u9650\u5728\uff1acache D\u548c\u5b83\u7684\u4e0a\u4e00\u4e2acache\u7ed3\u70b9\uff08\u5373cache B\uff09 \u4e4b\u95f4\u7684\u5bf9\u8c61\uff0c\u8fd9\u4e9b\u5bf9\u8c61\u4f1a\u88ab\u6620\u5c04\u5230\u65b0cache\u4e0a\u53bb\uff1bcache B\u4e4b\u524d\u548ccache D\u4e4b\u540e\u7684\u5bf9\u8c61\u90fd\u4e0d\u4f1a\u53d7\u5f71\u54cd\u3002<\/p>\n<\/li>\n<li>\n<p>\u5f53\u79fb\u9664\u4e00\u4e2aceche B\u65f6\uff0cB\u548cA\u4e4b\u95f4\u7684\u5bf9\u8c61\u4f1a\u88ab\u6620\u5c04\u5230B\u7684\u4e0b\u4e00\u4e2a\u7ed3\u70b9C\u4e0a\u53bb\u3002B\u548cC\u4e4b\u95f4\u7684\u53caA\u4e4b\u524d\u7684\u5bf9\u8c61\u4e5f\u4e0d\u4f1a\u53d7\u5f71\u54cd\u3002<\/p>\n<\/li>\n<\/ul>\n<p>\u66f4\u591a\u8be6\u7ec6\u4ecb\u7ecd\u53ef\u53c2\u8003\uff1a<a href=\"http:\/\/blog.csdn.net\/sparkliang\/article\/details\/5279393\">\u4e00\u81f4\u6027hash\u7b97\u6cd5 &#8211; consistent hashing <\/a><\/p>\n<h3>\u54c8\u5e0c\u78b0\u649e\u653b\u51fb<\/h3>\n<p>\u54c8\u5e0c\u78b0\u649e\u653b\u51fb\u662f\u6307\uff1a\u5bf9\u4e8e\u4f7f\u7528\u94fe\u63a5\u6cd5\u89e3\u51b3\u78b0\u649e\u7684\u6563\u5217\u8868\u5b9e\u73b0\uff0c\u901a\u8fc7\u7cbe\u5fc3\u6784\u5efa\u4e00\u7ec4\u5bf9\u8c61\uff0c\u4f7f\u8fd9\u4e9b\u5bf9\u8c61\u6620\u5c04\u5230\u540c\u4e00\u4e2a\u69fd\u4f4d\uff0c\u4ece\u800c\u4f7f\u6563\u5217\u8868\u9000\u5316\u4e3a\u4e00\u4e2a\u94fe\u8868\uff0c\u7531\u4e8e\u94fe\u8868\u7684\u64cd\u4f5c\u6548\u7387\u5e73\u5747\u6bd4\u6563\u5217\u8868\u4f4e\uff0c\u4ece\u800c\u5bfc\u81f4\u6563\u5217\u8868\u7684\u6027\u80fd\u4e0b\u964d\uff0c\u8fdb\u800c\u8ba9\u6574\u4e2a\u5e94\u7528\u7a0b\u5e8f\u7684\u6027\u80fd\u4ee5\u7ea7\u6570\u4e0b\u964d\u3002<\/p>\n<p>\u5173\u4e8e\u901a\u8fc7\u54c8\u5e0c\u78b0\u649e\u653b\u51fb\u7684\u53ef\u4ee5\u53c2\u8003\u8fd9\u7bc7\u6587\u7ae0\uff1a<a href=\"http:\/\/coolshell.cn\/articles\/6424.html\">Hash Collision DoS \u95ee\u9898<\/a><\/p>\n<h2>Java\u91cc\u7684\u6563\u5217<\/h2>\n<p><code>java.util.HashMap<\/code>\u7c7b\u662fJDK\u91cc\u7684\u6563\u5217\u8868\u5b9e\u73b0\uff0c\u5b83\u7684\u5b9e\u73b0\u65b9\u5f0f\u662f\u69fd+\u94fe\u8868\uff0c\u4e5f\u5c31\u662f\u7528\u94fe\u63a5\u6cd5\u89e3\u51b3\u78b0\u649e\u3002<\/p>\n<p>\u5b83\u7684\u6563\u5217\u7b97\u6cd5\u662f\u9664\u6cd5\u6563\u5217\u7684\u601d\u60f3\uff0c\u4e0e\u5927\u591a\u6570\u6559\u79d1\u4e66\u91cc\u8bb2\u7684\u4e0d\u540c\u662f\uff0c\u5b83\u7684\u69fd\u7684\u957f\u5ea6\u662f2\u7684\u6574\u6570\u6b21\u5e42\uff0c\u800c\u4e0d\u662f\u4e00\u4e2a\u8d28\u6570\uff1b\u4e14\u7528\u6309\u4f4d\u4e0e\u8fd0\u7b97\u4ee3\u66ff\u9664\u6cd5\uff1a<\/p>\n<pre><code class=\"java\">\/\/  \u8ba1\u7b97\u7ed9\u5b9a\u54c8\u5e0c\u503ch\u6240\u5bf9\u5e94\u7684\u69fd\u4e0b\u6807\nstatic int indexFor(int h, int length) {\n    \/\/ assert Integer.bitCount(length) == 1 : \"length must be a non-zero power of 2\";\n    return h &amp; (length-1);\n}\n<\/code><\/pre>\n<p>h\u662f\u5bf9\u8c61\u7684\u54c8\u5e0c\u503c\uff0clength\u662f\u69fd\u7684\u957f\u5ea6\u3002\u8fd9\u6837\u505a\u4e3b\u8981\u662f\u51fa\u4e8e\u6027\u80fd\u7684\u8003\u8651\u3002<\/p>\n<p>\u5bf9\u4e8e\u54c8\u5e0c\u78b0\u649e\u653b\u51fb\uff0c<code>java.util.HashMap<\/code>\u7c7b\u4eceJDK1.8\u5f00\u59cb\u4f1a\u5728\u94fe\u8868\u7684\u957f\u5ea6\u8fbe\u5230\u67d0\u4e2a\u9600\u503c\u65f6\uff0c\u5c06\u6563\u5217\u8868\u7684\u5b9e\u73b0\u8f6c\u6362\u4e3a\u4e00\u4e2a\u5b9a\u5236\u7684\u7ea2\u9ed1\u6811\u3002<\/p>\n<p>\u5982\u679c\u5bf9\u4e86\u89e3\u66f4\u591a\uff0c\u5f53\u7136\u5e94\u8be5\u901a\u8fc7google\u53bb\u67e5\u627e\u66f4\u591a\u8d44\u6599\u3002<\/p>\n<hr\/>\n<p>\u6b22\u8fce\u5173\u6ce8\u6211\u7684\u5fae\u4fe1\u516c\u4f17\u53f7: <strong>coderbee\u7b14\u8bb0<\/strong>\uff0c\u53ef\u4ee5\u66f4\u53ca\u65f6\u56de\u590d\u4f60\u7684\u8ba8\u8bba\u3002<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"258\" height=\"258\" src=\"https:\/\/coderbee.net\/wp-content\/uploads\/2019\/01\/coderbee-note.jpg\" class=\"alignnone size-full wp-image-1707\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u6563\u5217\u4e00\u822c\u4e5f\u53eb\u54c8\u5e0c\u3002\u6563\u5217\u8868\u4e5f\u53eb\u54c8\u5e0c\u8868\u3002\u672c\u4f4d\u5c06\u4ecb\u7ecd\u6563\u5217\u8868\u7684\u57fa\u672c\u77e5\u8bc6\u3001\u4e00\u81f4\u6027\u54c8\u5e0c\u3001\u54c8\u5e0c &hellip; <a href=\"https:\/\/coderbee.net\/index.php\/algorithm\/20130919\/479\">\u7ee7\u7eed\u9605\u8bfb <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[53],"tags":[93,55,56],"_links":{"self":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/479"}],"collection":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/comments?post=479"}],"version-history":[{"count":4,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/479\/revisions"}],"predecessor-version":[{"id":484,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/479\/revisions\/484"}],"wp:attachment":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/media?parent=479"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/categories?post=479"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/tags?post=479"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}