179-最大数

public String largestNumber(int[] nums) {
    String[] strArr = new String[nums.length];
    for (int i = 0; i < strArr.length; i++) {
        strArr[i] = String.valueOf(nums[i]);
    }

    Arrays.sort(strArr, (o1, o2) -> (int) (Long.parseLong(o1 + o2) - Long.parseLong(o2 + o1)));	//就这句,这里的o1 + o2是字符串拼接
    StringBuilder sb = new StringBuilder();
    boolean flag = true;
    for(int i = strArr.length - 1; i >= 0; i--){
        sb.append(strArr[i]);
        if (!"0".equals(strArr[i])) flag = false;
    }
    if (flag) return "0";
    return sb.toString();
}

public String largestNumber(int[] nums) {
    String[] strArr = new String[nums.length];
    for (int i = 0; i < strArr.length; i++) {
        strArr[i] = String.valueOf(nums[i]);
    }

    Arrays.sort(strArr, (o1, o2) -> (o1 + o2).compareTo(o2 + o1));
    StringBuilder sb = new StringBuilder();
    boolean flag = true;
    for(int i = strArr.length - 1; i >= 0; i--){
        sb.append(strArr[i]);
        if (!"0".equals(strArr[i])) flag = false;
    }
    if (flag) return "0";
    return sb.toString();
}