剑指offer-42-翻转单词顺序列

问题难度适中，这里说一下开头结尾空格的处理。

    public String ReverseSentence(String str) {

        if(str==null)

            return null;

        char[] data =str.toCharArray();

        if(data.length==0)

            return "";

        int leftMin=0,rightMax=data.length-1;

        while(leftMin<=data.length-1&&data[leftMin]==' '){

            leftMin++;

        }

        while(rightMax>=0&&data[rightMax]==' '){

            rightMax--;

        }

        reverseArray(data,leftMin,rightMax);

        int left=leftMin,right=leftMin;

        while(right<=rightMax){

            if(data[right]==' '||right==rightMax){

                if(right==rightMax)

                    reverseArray(data,left,right);

                else

                    reverseArray(data,left,right-1);

                left=right+1;

                right++;

            }else if(data[left]==' '){

                left++;

            }else{

                right++;

            }

        }

        return new String(data);

    }

开头结尾字符串不翻转

" abc" -> " abc"

"abc " -> "abc "

思路：直接反转的时候略去开头结尾的空格。

---

    public String ReverseSentence(String str) {

        if(str==null)

            return null;

        char[] data =str.toCharArray();

        if(data.length==0)

            return "";

        reverseArray(data,0,data.length-1);

        int left=0,right=0;

        while(right<data.length){

            if(data[right]==' '||right==data.length-1){

                if(right==data.length-1&&data[right]!=' ')

                    reverseArray(data,left,right);

                else

                    reverseArray(data,left,right-1);

                left=right+1;

                right++;

            }else if(data[left]==' '){

                left++;

            }else{

                right++;

            }

        }

        return new String(data);

    }

开头结尾字符串翻转

" abc" -> "abc "

"abc " -> " abc"

思路：全部反转的时候，空格已经翻转了，只需要保证翻转单词时候不翻转即可。翻转后在开头的，程序会直接略去；在结尾的，添加data[right]!=' '条件即可。

    public void reverseArray(char[] array,int start,int end){
        char temp ='0';
        while(start<end){
            temp = array[start];
            array[start] = array[end];
            array[end] = temp;
            start++;
            end--;
        }
    }