题目
给定三个字符串str from和to，把str中所有from的子串全部替换成to字符串，对连续出现from的部分要求只替换成一个to字符串，返回最终的结果字符串。
举例
str = “123abc” from=“abc” to=“4567” 返回 1234567
str=“123” from=“abc” to=“456” 返回123
str=“123abcabc” from=“abc” to=“X” 返回123X
public class REPLACE {public static void main(String[] args) {String str = "123abc";String from = "abc";String to = "4567";System.out.println(new REPLACE().replace(str, from, to));}public String replace(String str, String from, String to) {if (str == null || from == null || to == null || str.equals("") || from.equals("")) {return str;}char[] chas = str.toCharArray();char[] chaf = from.toCharArray();int match = 0;for (int i = 0; i < chas.length; i++) {if (chas[i] == chaf[match++]) {if (match == chaf.length) {clear(chas, i , chaf.length);match = 0;}}else { // 出现不匹配的字符，重置matchmatch = 0;}}String res ="" ;String cur ="";for (int i = 0; i < chas.length; i++) {if (chas[i] != 0) {cur += chas[i];}if (chas[i] == 0 && (i == 0 || chas[i-1] != 0)){res = res + cur + to;cur = "";}}if (!cur.equals("")){res = res + cur;}return res;}public void clear ( char[] chas, int end, int len){while (len-- != 0) {chas[end--] = 0;}}
}
