[英]Binary search implementation java algorithm
我需要實現二進制搜索算法的幫助,有人可以告訴我我的代碼有什么問題:
public int bsearch(Item idToSearch) {
int lowerBoundary = 0;
int upperBoundary = myStore.size() - 1;
int mid = -1;
while(upperBoundary >= lowerBoundary) {
mid = (lowerBoundary + upperBoundary) / 2;
//if element at middle is less than item to be searched, than set new lower boundary to mid
if(myStore.get(mid).compareTo(idToSearch) < 0) {
lowerBoundary = mid - 1;
} else {
upperBoundary = mid + 1;
}
} //end while loop
if(myStore.get(mid).equals(idToSearch)) {
return mid;
} else {
return -1; // item not found
}
} // end method
我認為您在更新lowerBoundary
和upperBoundary
時犯了一個錯誤。
可能是:
if(myStore.get(mid).compareTo(idToSearch) < 0){
lowerBoundary = mid + 1;
} else {
upperBoundary = mid - 1;
}
而且,如果在mid
找到元素,為什么不中斷循環呢?
我會
mid = (hi + lo) >>> 1;
以避免溢出導致錯誤。 第一個問題是邊界,如果他發現了價值,也應該停下來,但他不會這樣做,否則可能會被忽視。
while(upperBoundary >= lowerBoundary)
{
mid = (lowerBoundary + upperBoundary) / 2;
if (myStore.get(mid).equals(idToSearch)) break; // goal
if(myStore.get(mid).compareTo(idToSearch) < 0)
{
lowerBoundary = mid + 1;
}
else
{
upperBoundary = mid - 1;
}
}
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