标签：des style blog class code java tar javascript ext strong get
Given an array of integers, find two numbers such that they add up to a specific target number.
The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.
You may assume that each input would have exactly one solution.
Input: numbers={2, 7, 11, 15},
target=9
Output: index1=1, index2=2
Naive Approach:
1 public int[] twoSum(int[] numbers, int target) { 2 //Note this is the naive apporach 3 //the time complexity is n^2. 4 int[] result = new int[2]; 5 for (int i = 0; i < numbers.length; i++) { 6 for (int j = i + 1; j < numbers.length; j++) { 7 if (target == numbers[i] + numbers[j]) { 8 //Note 9 result[0] = i + 1; 10 result[1] = j + 1; 11 return result; 12 } 13 } 14 } 15 return result; 16 }
Using Hash-Map
1 public int[] twoSum(int[] numbers, int target) { 2 int[] result = new int[2]; 3 HashMap<Integer,Integer> map = new HashMap<Integer, Integer>(); 4 for(int i= 0;i<numbers.length;i++){ 5 if(map.containsKey(numbers[i])){ 6 result[0]=map.get(numbers[i]); 7 result[1]=i+1; 8 } 9 else { 10 map.put((target-numbers[i]),i+1); 11 } 12 } 13 return result; 14 }
Basic method of HashMap
http://docs.oracle.com/javase/7/docs/api/java/util/HashMap.html
| Modifier and Type | Method and Description |
|---|---|
void |
clear()
Removes all of the mappings from this map. |
Object |
clone()
Returns a shallow copy of
this HashMap instance: the keys and values themselves
are not cloned. |
boolean |
containsKey(Object key)
Returns true if this map contains a
mapping for the specified key. |
boolean |
containsValue(Object value)
Returns true if this map maps one or
more keys to the specified value. |
Set<Map.Entry<K,V>> |
entrySet()
Returns a Set view
of the mappings contained in this map. |
V |
get(Object key)
Returns the value to which the specified key is mapped,
or null if this map contains no mapping for the
key. |
boolean |
isEmpty()
Returns true if this map contains no
key-value mappings. |
Set<K> |
keySet()
Returns a Set view
of the keys contained in this map. |
V |
put(K key, V value)
Associates the specified value with the specified key
in this map. |
void |
putAll(Map<?
extends K,?
extends V> m)
Copies all of the mappings from the specified map to
this map. |
V |
remove(Object key)
Removes the mapping for the specified key from this map
if present. |
int |
size()
Returns the number of key-value mappings in this
map. |
Collection<V> |
values()
Returns a Collection view
of the values contained in this map. |
标签：des style blog class code java tar javascript ext strong get
原文地址：http://www.cnblogs.com/Altaszzz/p/3702504.html
