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Regarding complexity (if comparison based sorting algorithm used)

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问题 as we all know that any sorting algorithm based on comparison model has lower bound of nlogn i.e Omega(nlogn). which can be proved mathematically. but as we all know dutch flag problem can sort 3 distinct elements (used repeatedly) in O(n) time.It is also based on comparison model but can sort in O(n) time. so how can we justify lower bound of sorting based on comparison model , because dutch flag problem kinda violates that. please help me understanding the difference..... Thanks 回答1: In my

rationale for std::lower_bound and std::upper_bound?

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问题 STL provides binary search functions std::lower_bound and std::upper_bound, but I tend not to use them because I've been unable to remember what they do, because their contracts seem completely mystifying to me. Just from looking at the names, I'd guess that "lower_bound" might be short for "last lower bound", i.e. the last element in the sorted list that is <= the given val (if any). And similarly I'd guess "upper_bound" might be short for "first upper bound", i.e. the first element in the

regex (java) match numbers equal or greater than 20, incremented by 5, no leading zeros allowed

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问题 I am a new user, so excuse if this question should be answered in it's original post: regex match numbers greater or equal than 20, by increments of 5, range 20 to 999 Neverteless, here is the current question: Match all numbers equal or greater then 20 (no upper limit) Increments of 5 No decimal point Leading zeros shouldn't be allowed With stackoverflow user YMI response on another post: (\d{2}|[2-9])[05] and user nhahtdh ^([2-9]|[1-9]\d)[05]$ However I would like to explorer the option of

Upper/lower bounds don't work as I expect, can not understand why

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问题 Here is the code. As a result I get "4 4". Don't understand why it is not "2 4" (according to lower and upper bounds' defenitions). #include <bits/stdc++.h> using namespace std; int main() { vector<int> v = {1, 2, 4, 5}; vector<int>::iterator s , f; s = lower_bound(v.begin(), v.end(), 3); f = upper_bound(v.begin(), v.end(), 3); cout << (*s) << " " << (*f); return 0; } 回答1: From std::lower_bound: Returns an iterator pointing to the first element in the range [first,last) which does not compare

rationale for std::lower_bound and std::upper_bound?

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STL provides binary search functions std::lower_bound and std::upper_bound, but I tend not to use them because I've been unable to remember what they do, because their contracts seem completely mystifying to me. Just from looking at the names, I'd guess that "lower_bound" might be short for "last lower bound", i.e. the last element in the sorted list that is <= the given val (if any). And similarly I'd guess "upper_bound" might be short for "first upper bound", i.e. the first element in the sorted list that is >= the given val (if any). But the documentation says they do something rather

STL MAP should use find() or [n] identifier to find element in map?

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问题 I am confused which is more efficient? As we can access map directly, why do we need to use find? I just need to know which way is more efficient. #include <iostream> #include <map> using namespace std; int main () { map<char,int> mymap; map<char,int>::iterator it; mymap['a']=50; mymap['b']=100; mymap['c']=150; mymap['d']=200; //one way it=mymap.find('b'); cout << (*it).second <<endl; //another way cout << mymap['b'] <<endl; return 0; } thanks in advance! :) 回答1: Using find means that you don

Difference between basic binary search for upper bound and lower bound?

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In the article http://community.topcoder.com/tc?module=Static&d1=tutorials&d2=binarySearch , the author discusses binary search. He makes a distinction between finding the lowest value where something is true, and the highest value where something is false. The array being searched looks something like: false false false true true I am curious as to why these two cases are different. Why can't you just find the lowest value which is true, then subtract one to find the highest value which is false? Edit2: Ok, so I understand lower vs upper bound. Now, I am struggling to understand, when

Difference between basic binary search for upper bound and lower bound?

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问题 In the article http://community.topcoder.com/tc?module=Static&d1=tutorials&d2=binarySearch, the author discusses binary search. He makes a distinction between finding the lowest value where something is true, and the highest value where something is false. The array being searched looks something like: false false false true true I am curious as to why these two cases are different. Why can't you just find the lowest value which is true, then subtract one to find the highest value which is

Java equivalent of c++ equal_range (or lower_bound & upper_bound)

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I have a List of object sorted and I want to find the first occurrence and the last occurrence of an object. In C++, I can easily use std::equal_range (or just one lower_bound and one upper_bound). For example: bool mygreater (int i,int j) { return (i>j); } int main () { int myints[] = {10,20,30,30,20,10,10,20}; std::vector<int> v(myints,myints+8); // 10 20 30 30 20 10 10 20 std::pair<std::vector<int>::iterator,std::vector<int>::iterator> bounds; // using default comparison: std::sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30 bounds=std::equal_range (v.begin(), v.end(), 20); // ^ ^ //

STL MAP should use find() or [n] identifier to find element in map?

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I am confused which is more efficient? As we can access map directly, why do we need to use find? I just need to know which way is more efficient. #include <iostream> #include <map> using namespace std; int main () { map<char,int> mymap; map<char,int>::iterator it; mymap['a']=50; mymap['b']=100; mymap['c']=150; mymap['d']=200; //one way it=mymap.find('b'); cout << (*it).second <<endl; //another way cout << mymap['b'] <<endl; return 0; } thanks in advance! :) Using find means that you don't inadvertently create a new element in the map if the key doesn't exist, and -- more importantly -- this