Plus One

public int[] plusOne(int[] digits) {
    int carries = 1;
    for(int i=digits.length-1; i>=0 && carries>0; i--){
        int sum = digits[i] + carries;
        digits[i] = sum % 10; 
        carries = sum / 10; //进位
    }
    if(carries==0){ //加完最高位后，判断carries是否为0
        return digits;
    }
    // carries == 1
    int[] rst = new int[digits.length+1];
    rst[0] = 1;
    for(int i=1; i<rst.length; i++){
        rst[i] = digits[i-1];
    }
    return rst;
}