binary-search

问题 I'm learning algorithms/big o and i was just curious about this. The use of mid = (low+high)/2; in order to get the midpoint for a binary search algorithm is generally discouraged because of the possibility of an overflow error. Why would this cause an overflow error to occur, and how does mid = low + (high-low)/2; prevent this error? Thanks. 回答1: In the first case you calculate the value (low+high) which might be too huge to fit into an int, if low and high are both huge enough (say if both

问题 I am implementing binary search in C++. Here is my code: #include <iostream> #include <vector> #include <algorithm> using namespace std; int bs(vector<int> a, int val) { int l =0, r = a.size()-1; while(l<=r) // Significance of == { int mid = l + (r-l)/2; if(a[mid]==val) return mid; if(a[mid]>val) { r = mid-1; continue; } else { l = mid + 1 ; } } return l; // Deliberately returning this } int main() { vector<int> a = {1,3}; cout << bs(a,1) <<endl; return 0; } Question 1 In some implementations

问题 Here is my attempt at implementing the binary search that must follow: static <T> int binarySearch(List<? extends Comparable<? super T>> list, T key) static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) However, I would like to avoid code duplication and delegate one of the implementations to the other (currently, the first to the second). To do that I need to get rid of the wildcard ? and use a second generic type like so: public class BinarySearch { public

问题 This question already has answers here : Collections.binarySearch() vs. List indexOf() (3 answers) Closed 4 years ago . I have an array list of strings, the string are in sorted order, i want to find the index of a particular element, Which one will be faster? Performing indexOf() of lists Performing a binary search in an equivalent array? 回答1: You can use Collections.binarySearch directly for better efficience: public static <T> int binarySearch(List<? extends Comparable<? super T>> list, T

问题 I have created a List where I have kept some strings. But when I am doing binary search within this list, it is returning negative values while the item is in the list . So far my knowledge positive value will be returned when item in the list . But for some items it is returning negative and for some items positive. Code: @Test public void hello() { // List<String> arlst = new ArrayList<String>(); List arlst = new ArrayList(); arlst.add("TP"); arlst.add("PROVIDES"); arlst.add("QUALITY");

问题 Finding the maximum or minimum value in a sequence that increases montonically and then decreases monotonically can be done in O(log n). However, if i want to check if a number exists in such a sequence, can this also be done in O(log n)? I do not think that is possible. Consider this example: 1 4 5 6 7 10 8 3 2 0. In this example, if I need to find whether the sequence contains '2', I do not have any conditions to divide the search space into half of the original search space. In the worst,

问题 I have the following class: struct EdgeExtended { int neighborNodeId; int weight; int arrayPointer; bool isCrossEdge; }; I want to have a vector of such objects, sort it by neighborNodeId. Then I want to search for a particular neighborNodeId and return a reference to the found object inside the vector by binary search. Previously I used a map for that, so it was something like that: map<int, EdgeExtended> neighbours; ..... auto it = neighbours.find(dnodeId); if (it != neighbours.end()) {

问题 I have the following class: struct EdgeExtended { int neighborNodeId; int weight; int arrayPointer; bool isCrossEdge; }; I want to have a vector of such objects, sort it by neighborNodeId. Then I want to search for a particular neighborNodeId and return a reference to the found object inside the vector by binary search. Previously I used a map for that, so it was something like that: map<int, EdgeExtended> neighbours; ..... auto it = neighbours.find(dnodeId); if (it != neighbours.end()) {

问题 Hi, what is the index of the search key if we search for 24 in the following array using binary search. array = [10,20,21,24,24,24,24,24,30,40,45] I have a doubt regarding binary search that how does it works if a array has duplicate values.Can anybody clarify... 回答1: The array you proposed has the target value in the middle index, and in the most efficient implementations will return this value before the first level of recursion. This implementation would return '5' (the middle index). To

问题 If binarySearch method requires you to sort your array before passing it as parameter to the method call, why not do a sort in the binarySearch method? 回答1: Binary search works by assuming the middle of the array contains the median value in the array. If it is not sorted, this assumption does not make sense, since the median can be anywhere and cutting the array in half could mean that you cut off the number you were searching for. The reason binary search does not do the sort itself is