LeetCode75 1768.交替合并字符串

1768.交替合并字符串
https://leetcode.cn/problems/merge-strings-alternately/description/?envType=study-plan-v2&envId=leetcode-75

public String mergeAlternately(String word1, String word2) {
        int len1 = word1.length();
        int len2 = word2.length();
        StringBuilder stringBuilder = new StringBuilder();
        int i = 0, j = 0;
        while (i < len1 && j < len2){
            stringBuilder.append(word1.charAt(i)).append(word2.charAt(j));
            i++;
            j++;
        }
        if (i == len1 && j == len2) return stringBuilder.toString();
        if (i == len1){
            stringBuilder.append(word2.substring(j,len2));
        }else {
            stringBuilder.append(word1.substring(i,len1));
        }
        return stringBuilder.toString();
    }

总结：这种构造新字符串的使用StringBuilder类很方便 ，String类的substring方法是左闭右开的方法。