题目

方法

首先找到一个包含所有T的窗口，逐步右移。使用begin和end来标记窗口的起始。

    public String minWindow(String S, String T) {
        if (S == null || T == null) {
        	return null;
        }
        if (T.equals("") || S.equals("")) {
        	return "";
        }
        Map<Character, Integer> needFind = new HashMap<Character, Integer>();
        Map<Character, Integer> hasFind = new HashMap<Character, Integer>();
        
        int lenS = S.length();
        int lenT = T.length();
        for (int i = 0; i < lenT; i++) {
        	char ch = T.charAt(i);
        	if (!needFind.containsKey(ch)) {
        		needFind.put(ch, 1);
        		hasFind.put(ch, 0);
        	} else {
        		needFind.put(ch, needFind.get(ch) + 1);
        	}
        }
        
        int newBegin = -1;
        int newEnd = S.length();
        int count = 0;
        for (int begin = 0, end = 0; end < lenS; end++) {
        	char ch = S.charAt(end);
        	if (needFind.containsKey(ch)) {
        		hasFind.put(ch, hasFind.get(ch) + 1);
        		if (hasFind.get(ch) <= needFind.get(ch)) {
        			count++;
        		}
        		if (count == lenT) {
        			char temp = S.charAt(begin);
        			while(!needFind.containsKey(temp) || hasFind.get(temp) > needFind.get(temp)) {
        				
        				if (needFind.containsKey(temp) && hasFind.get(temp) > needFind.get(temp)) {
        					hasFind.put(temp, hasFind.get(temp) - 1);
        				}
        				
        				begin = begin + 1;
        				temp = S.charAt(begin);
        			}
        			
        			if (end - begin < newEnd - newBegin) {
        				newEnd = end;
        				newBegin = begin;
        			}
        		}
        	}
        }
        
        if (newBegin == -1) {
        	return "";
        } else {
        	return S.substring(newBegin, newEnd + 1);
        }       
    }

Minimum Window Substring,布布扣,bubuko.com

Minimum Window Substring

原文：http://blog.csdn.net/u010378705/article/details/35572759