数据结构复习10.刷题常用点总结

Integer.bitCount(int i)
一. Array
(1) array.length; //没有括号
(2) Reference类型注意检测null
(3) Arrays.sort(a);//排序
(4) Arrays.toString(a)//print
(5) copy:
a = Arrays.copyOf(b, b.length);
System.arrayCopy(a, 0, b, 0, b.length);
(6) print: System.out.println(Arrays.toString(a));
(7) Arrays.fill()填充一段数组
Arrays.fill(E[] a, E b);
Arrays.fill(E[] a, E b, int fromIndex, int toIndex)
二. 通用二分查找
public class BinarySearch {
public static void main(String[] args) {
int[] a = {1, 2, 3};
System.out.println(binarySearch(a, 2));
}
static int binarySearch(int[] A, int target) {
if (A.length == 0) {
return -1;
}

    int start = 0;
    int end = A.length - 1; //注意-1
    int mid;
    while (start + 1 < end) { //注意是+1
        mid = start + (end - start) / 2;
        if (A[mid] == target) {
            end = mid; //如果不找第一个，可以直接返回。
        } else if (A[mid] < target){
            start = mid;
        } else {
            end = mid;
        }
    }

    //注意输出
    if (A[start] == target) {
        return start;
    }
    if (A[end] == target) {
        return end;
    }
    return -1;
}

}

三. ArrayList
add(Object);
add(index, Object);
set(index, Object);
get(index);
remove(index);
size();
反转list， Collections.reverse(res);

四. LinkedList
addFirst(Object);
addLast(Object);
getFirst();
getLast();
removeFirst();
removeLast();
add(index，Object);
反转list， Collections.reverse(res);

五. iterator
List numbers = new LinkedList();
numbers.add(1);
Iterator itr = numbers.iterator();
迭代器使用期间，不能添加/删除元素。否则回报错 java.util.ConcurrentModificationException。

六. Stack
push();
pop();
peek();
isEmpty();

七. Queue
offer();
poll();
peek();
isEmpty();

八.compare
1. comparator
Collections.sort(listA, new myComparator() {
@override
public int compare(Myclass obj1, Myclass obj2) {
return 1;
}
})
2. comparable
public class Myclass implements Comparable{
@override
public int compareTo(Myclass obj2) {
return 1;
}
}

九. Hash
1.HashMap
map.keySet();//得到键set
map.entrySet();//得到value集合
map.values()//返回一个值的集合
map.containsKey(key);
put(key, value)
get(key)
2.HashSet
add(key);
contains(key);
iterator()

十.Tree
1.TreeMap and TreeSet
public static void main(String args[]) {

  /* This is how to declare TreeMap */
  TreeMap tmap = 
         new TreeMap();

  /*Adding elements to TreeMap*/
  tmap.put(1, "Data1");
  tmap.put(23, "Data2");
  tmap.put(70, "Data3");
  tmap.put(4, "Data4");
  tmap.put(2, "Data5");

  /* Display content using Iterator*/
  Set set = tmap.entrySet();
  Iterator iterator = set.iterator();
  while(iterator.hasNext()) {
     Map.Entry mentry = (Map.Entry)iterator.next();
     System.out.print("key is: "+ mentry.getKey() + " & Value is: ");
     System.out.println(mentry.getValue());
  }

}
or
new TreeMap