[LintCode] Space Replacement

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.

Example

Given "Mr John Smith", length = 13.

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

Analysis: We can know the length after the replacement. And then we just need to fill in the new space from end to beginning of the word.

class Solution {
public:
    int replaceBlank(char string[], int length) {
        if(0==length) return 0;
        int num = 0;
        for(int i=0;i<length;i++){
            if(string[i] == ' ') num++;
        }
        
        int newLen = length + num*2;
        string[newLen] = 0;
        int j = 1;
        for(int i=length-1;i>=0;i--){
            if(string[i] != ' '){
                string[newLen - j] = string[i];
                j++;
            }
            else{
                string[newLen - j] = '0';
                j++;
                string[newLen - j] = '2';
                j++;
                string[newLen - j] = '%';
                j++; 
            }
        }
        return newLen;
    }
};