Consecutive Ones - Amazon Top Interview Questions

Problem Statement :

You are given a list of integers nums which contains at least one 1. Return whether all the 1s appear consecutively.


1 ≤ n ≤ 100,000 where n is the length of nums

Example 1


nums = [0, 1, 1, 1, 2, 3]



All the 1s appear consecutively here in the middle.

Solution :


                        Solution in C++ :

bool solve(vector<int>& nums) {
    for (int i = 0, prev = -1; i < nums.size(); i++) {
        if (nums[i] == 1) {
            if (prev != -1 && i - prev > 1)
                return false;
                prev = i;
    return true;

                        Solution in Java :

import java.util.*;

class Solution {
    public boolean solve(int[] nums) {
        int f = -1;
        int l = -1;
        int c = 0;
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] == 1) {
                if (f == -1) {
                    f = i;
                l = i;
        return (c == l - f + 1);

                        Solution in Python : 
class Solution:
    def solve(self, nums):
        alreadyseen = 0
        0 means never seen
        1 means currently seeing
        2 means has finished seeing
        for x in nums:
            if x == 1:
                if alreadyseen == 2:
                    return False
                alreadyseen = 1
            elif alreadyseen:
                alreadyseen = 2
        return True

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