lintcode-medium-Minimum Window Substring

public class Solution {
    /**
     * @param source: A string
     * @param target: A string
     * @return: A string denote the minimum window
     *          Return "" if there is no such a string
     */
    public String minWindow(String source, String target) {
        // write your code
        
        if(source == null || source.length() == 0 || target == null || target.length() == 0 || source.length() < target.length())
            return "";
        
        int[] tar = new int[128];
        int[] sou = new int[128];
        
        for(int i = 0; i < target.length(); i++)
            tar[target.charAt(i)]++;
        
        int left = 0;
        int right = 0;
        int start = -1;
        int end = source.length();
        int win = 0;
        
        int len = source.length();
        
        for(; right < len; right++){
            if(tar[source.charAt(right)] != 0){
                sou[source.charAt(right)]++;
                
                if(sou[source.charAt(right)] <= tar[source.charAt(right)]){
                    win++;
                }
                
                if(win == target.length()){
                    while(left < right){
                        if(tar[source.charAt(left)] == 0){
                            left++;
                        }
                        else if(sou[source.charAt(left)] > tar[source.charAt(left)]){
                            sou[source.charAt(left)]--;
                            left++;
                        }
                        else{
                            break;
                        }
                    }
                    
                    win--;
                    
                    if(right - left < end - start){
                        start = left;
                        end = right;
                    }
                }
                
            }
        }
        
        
        if(start == -1)
            return "";
        else
            return source.substring(start, end + 1);
    }
}