[LintCode] Space Replacement

13651657101 發布于2019-08-14 15:15 / 2420人閱讀

摘要：，這里要注意循環的是前個元素，不是當前元素在循環條件里前移，新位置的指針在語句前移序數從后向前沒有空格也要把當前位元素移到新的位置

Problem

Write a method to replace all spaces in a string with %20. The string is given in a characters array, you can assume it has enough space for replacement and you are given the true length of the string.

You code should also return the new length of the string after replacement.

Example

Given "Mr John Smith", length = 13.

The string after replacement should be "Mr%20John%20Smith".

Note

If you are using Java or Python，please use characters array instead of string.

Challenge

Do it in-place.

Solution

It"s a easy problem but you are required to do it in-place.
No StringBuilder.

public class Solution {
    public int replaceBlank(char[] str, int length) {
        if (length == 0) return 0;
        int len = length;
        //calculate the new length after all the replacements
        for (int i = 0; i < len; i++) {
            if (str[i] == " ") {
                len += 2;
            }
        }
        int j = 1;
        //這里要注意：循環的是前length-1個元素，不是len-1
        for (int i = length - 1; i >= 0; i--) {
            //當前元素i--在for循環條件里前移，新位置的指針(len - j++)在if-else語句前移
            if (str[i] == " ") {
                //序數從后向前 len-1 len-2 len-3
                str[len - j++] = "0";
                str[len - j++] = "2";
                str[len - j++] = "%";
            }
            //沒有空格也要把當前位元素移到新的位置 
            else {
                str[len - j++] = str[i];
            }
        }
        return len;
    }
}

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