Intersection of Two Arrays II

Given two arrays, write a function to compute their intersection.

Example

Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2, 2].

利用较小的数组建m（下面代码并没有这个优化）注意当m为空时跳出循环 在nums2较大的情况下避免过多无用计算

public class Solution {
    /**
     * @param nums1 an integer array
     * @param nums2 an integer array
     * @return an integer array
     */
    public int[] intersection(int[] nums1, int[] nums2) {
        // Write your code here
        if(nums1==null||nums2==null) return null;
        
        if(nums1.length==0||nums2.length==0) return new int[0];
        
        Map<Integer, Integer> m = new HashMap<Integer, Integer>();
        Map<Integer, Integer> resM = new HashMap<Integer, Integer>();
        
        for(int i : nums1){
            if(m.containsKey(i)){
                m.put(i, m.get(i)+1);
            }else{
                m.put(i, 1);
            }
        }
        for(int i:nums2){
            if(m.containsKey(i)){
                if(m.get(i)==1){
                    m.remove(i);
                }else{
                    m.put(i, m.get(i)-1);
                }
                if(resM.containsKey(i)){
                    resM.put(i, resM.get(i)+1);
                }else{
                    resM.put(i, 1);
                }
                if(m.size()==0) break;
            }
        }
        List<Integer> res = new ArrayList();
        for(Map.Entry<Integer, Integer> entry: resM.entrySet()){
            int vCnt = entry.getValue();
            int key = entry.getKey();
            while(vCnt>0){
                res.add(key);
                vCnt--;
            }
        }
        int[] resInt = new int[res.size()];
        int index =0;
        for(Integer i : res){
            resInt[index++] = i;
        }
        return resInt;
    }
}