T(n) = 25T(n/5)+n^2的时间复杂度?

本文详细解析了递归公式T(n) = 25T(n/5) + n^2的时间复杂度,并通过主定理得出其为O(n^2*logn)。文中逐步展开递归过程,帮助理解递归函数的行为。

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  1. 原文地址:T(n) = 25T(n/5)+n^2的时间复杂度 作者:djkpengjun  
  2. 主定理:  
  3.   
  4. 对于T(n) = a*T(n/b)+c*n^k;T(1) = c 这样的递归关系,有这样的结论:   
  5. if (a > b^k)   T(n) = O(n^(logb(a)));logb(a)b为底a的对数  
  6. if (a = b^k)   T(n) = O(n^k*logn);  
  7. if (a < b^k)   T(n) = O(n^k);  
  8.   
  9. a=25; b = 5 ; k=2  
  10.   
  11. a==b^k 故T(n)=O(n^k*logn)=O(n^2*logn)  
  12.   
  13.   
  14. T(n) = 25T(n/5)+n^2   
  15. = 25(25T(n/25)+n^2/25)+n^2  
  16. = 625T(n/25)+n^2+n^2 = 625T(n/25) + 2n^2  
  17. = 25^2 * T( n/ ( 5^2 ) ) + 2 * n*n  
  18. = 625(25T(n/125)+n^2/625) + 2n^2  
  19. = 625*25*T(n/125) + 3n^2  
  20. = 25^3 * T( n/ ( 5^3 ) ) + 3 * n*n  
  21. = ....  
  22. = 25 ^ x * T( n / 5^x ) + x * n^2  
  23.   
  24. T(n) = 25T(n/5)+n^2  
  25. T(0) = 25T(0) + n^2 ==> T(0) = 0  
  26. T(1) = 25T(0)+n^2 ==> T(1) = 1  
  27.   
  28. x = lg 5 n  
  29.   
  30.   25 ^ x * T( n / 5^x ) + x * n^2  
  31. = n^2 * 1 + lg 5 n * n^2  
  32. = n^2*(lgn)  
let arr1 = [ { "groupMemberId": 100691, "rongUserId": "LML-57950341", "groupMemberImage": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:17:36:694/79.jpg", "nickName": "敏", "laoMaNo": 306688, "sex": null, "isFriend": false, "groupMemberType": "NORMAL", "groupMemberState": true, "hasManRelated": false, "hasWomenRelated": false, "showRelated": true, "joinGroupDate": "2024-12-25T11:16:31.000 0000", "groupRemindState": false, "allowedPrivateChat": true, "stopPrivateChat": true, "noPrivateChatUserNum": 0, "isShield": false, "flag": true }, { "groupMemberId": 100678, "rongUserId": "LML-14347419", "groupMemberImage": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:13:56:143/31.jpg", "nickName": "aaaa", "laoMaNo": 547636, "sex": null, "isFriend": false, "groupMemberType": "NORMAL", "groupMemberState": false, "hasManRelated": false, "hasWomenRelated": false, "showRelated": true, "joinGroupDate": "2024-12-25T02:31:27.000 0000", "groupRemindState": false, "allowedPrivateChat": false, "stopPrivateChat": true, "noPrivateChatUserNum": 0, "isShield": false, "flag": true }, { "groupMemberId": 100677, "rongUserId": "LML-21652619", "groupMemberImage": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:13:56:143/31.jpg", "nickName": "Chris", "laoMaNo": 917490, "sex": null, "isFriend": false, "groupMemberType": "NORMAL", "groupMemberState": true, "hasManRelated": false, "hasWomenRelated": false, "showRelated": true, "joinGroupDate": "2024-12-24T03:05:21.000 0000", "groupRemindState": false, "allowedPrivateChat": true, "stopPrivateChat": true, "noPrivateChatUserNum": 0, "isShield": false, "flag": true }, { "groupMemberId": 100638, "rongUserId": "LML-74370986", "groupMemberImage": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:13:56:134/10.jpg", "nickName": "Leo", "laoMaNo": 906259, "sex": null, "isFriend": false, "groupMemberType": "NORMAL", "groupMemberState": true, "hasManRelated": false, "hasWomenRelated": false, "showRelated": true, "joinGroupDate": "2024-12-20T08:31:18.000 0000", "groupRemindState": false, "allowedPrivateChat": true, "stopPrivateChat": true, "noPrivateChatUserNum": 0, "isShield": false, "flag": true }, { "groupMemberId": 100092, "rongUserId": "LML-24436764", "groupMemberImage": "http://image.laomahahaha.com/yyqc/20240730/upload_t1uohak97de6yvaxyoxt8rrd3cdh3kfz.jpg", "nickName": "哇咔咔", "laoMaNo": 145338, "sex": null, "isFriend": false, "groupMemberType": "NORMAL", "groupMemberState": true, "hasManRelated": false, "hasWomenRelated": false, "showRelated": true, "joinGroupDate": "2024-12-10T03:01:17.000 0000", "groupRemindState": false, "allowedPrivateChat": true, "stopPrivateChat": true, "noPrivateChatUserNum": 0, "isShield": false, "flag": true }, { "groupMemberId": 100035, "rongUserId": "LML-92216234", "groupMemberImage": "../../static/3.jpg", "nickName": "我不是家长", "laoMaNo": 629569, "sex": null, "isFriend": true, "groupMemberType": "NORMAL", "groupMemberState": true, "hasManRelated": false, "hasWomenRelated": false, "showRelated": true, "joinGroupDate": "2024-12-10T02:35:15.000 0000", "groupRemindState": false, "allowedPrivateChat": true, "stopPrivateChat": true, "noPrivateChatUserNum": 0, "isShield": false, "flag": true } ] let arr2 = [ { "groupNo": 66725586, "groupGroupingName": "1", "groupGroupingMemberNum": 5, "isGroupGroupingMember": false, "rongGroupId": "GROUP66725586", "group": [ { "groupGroupingMemberId": 100677, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:13:56:143/31.jpg", "joinGroupGroupingDate": "2025-06-26T08:14:49.000 0000", "nickName": "Chris" }, { "groupGroupingMemberId": 100011, "headPicture": "http://image-laomale.test.upcdn.net/yyqc/20240717/upload_vdhdfg3skcosyqcwl6nc2iqt8tyd25fd.png", "joinGroupGroupingDate": "2025-06-26T08:14:49.000 0000", "nickName": "该喝喝" }, { "groupGroupingMemberId": 99998, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:23:06:432/93.jpg", "joinGroupGroupingDate": "2025-06-26T08:14:49.000 0000", "nickName": "蜡笔小新" }, { "groupGroupingMemberId": 100000, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:23:06:362/65.png", "joinGroupGroupingDate": "2025-06-26T08:14:49.000 0000", "nickName": "冷眸" }, { "groupGroupingMemberId": 100691, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:17:36:694/79.jpg", "joinGroupGroupingDate": "2025-06-26T08:14:49.000 0000", "nickName": "敏" } ] }, { "groupNo": 66725586, "groupGroupingName": "2", "groupGroupingMemberNum": 6, "isGroupGroupingMember": false, "rongGroupId": "GROUP66725586", "group": [ { "groupGroupingMemberId": 100638, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:13:56:134/10.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:09.000 0000", "nickName": "Leo" }, { "groupGroupingMemberId": 99998, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:23:06:432/93.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:09.000 0000", "nickName": "蜡笔小新" }, { "groupGroupingMemberId": 100000, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:23:06:362/65.png", "joinGroupGroupingDate": "2025-06-26T08:15:09.000 0000", "nickName": "冷眸" }, { "groupGroupingMemberId": 100691, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:17:36:694/79.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:09.000 0000", "nickName": "敏" }, { "groupGroupingMemberId": 100091, "headPicture": "http://image.laomahahaha.com/yyqc/20240828/upload_shgeloxr0zgr03a5dyep1pq1tg1xeyvi.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:09.000 0000", "nickName": "暖阳" }, { "groupGroupingMemberId": 99999, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:13:56:143/31.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:09.000 0000", "nickName": "茄子豆角" } ] }, { "groupNo": 66725586, "groupGroupingName": "3", "groupGroupingMemberNum": 5, "isGroupGroupingMember": true, "rongGroupId": "GROUP66725586", "group": [ { "groupGroupingMemberId": 100035, "headPicture": "../../static/3.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:30.000 0000", "nickName": "我不是家长" }, { "groupGroupingMemberId": 100092, "headPicture": "http://image.laomahahaha.com/yyqc/20240730/upload_t1uohak97de6yvaxyoxt8rrd3cdh3kfz.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:30.000 0000", "nickName": "哇咔咔" }, { "groupGroupingMemberId": 100009, "headPicture": "../../static/8.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:30.000 0000", "nickName": "天大地大我是老大" }, { "groupGroupingMemberId": 100008, "headPicture": "http://image.laomahahaha.com/yyqc/20240828/upload_p7wg8dzkk104qzs38vreshu1s5yiz9s2.jpg", "joinGroupGroupingDate": "2025-06-26T08:15:30.000 0000", "nickName": "瀟雨萌" }, { "groupGroupingMemberId": 100001, "headPicture": "http://images.laomahahaha.com/App/laomaleImage/2024-09-06 16:17:36:657/1.png", "joinGroupGroupingDate": "2025-06-26T08:15:30.000 0000", "nickName": "张哥哥" } ] } ] 根据arr2 中 group内 groupGroupingMemberId 和 arr1 中 groupMemberId 进行判断 如果相等的话证明arr2中有arr中的这个值 就新增一个flag值 = true 不相等就是没有的时候 flag值 = false
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