Remove One Element to Make the Array Strictly Increasing

Remove One Element to Make the Array Strictly Increasing - Problem

Array Easy

Given a 0-indexed integer array nums, return true if it can be made strictly increasing after removing exactly one element, or false otherwise.

If the array is already strictly increasing, return true.

The array nums is strictly increasing if nums[i - 1] < nums[i] for each index (1 <= i < nums.length).

Input & Output

Example 1 — Can Remove One Element

$ Input: nums = [1,2,10,5,7]

› Output: true

💡 Note: Remove the element at index 2 (value 10) to get [1,2,5,7], which is strictly increasing: 1 < 2 < 5 < 7

Example 2 — Already Strictly Increasing

$ Input: nums = [2,3,1,2]

› Output: false

💡 Note: No single removal can make this strictly increasing. Removing any one element still leaves violations

Example 3 — Already Strictly Increasing

$ Input: nums = [1,2,3]

› Output: true

💡 Note: Already strictly increasing: 1 < 2 < 3, so return true

Constraints

2 ≤ nums.length ≤ 1000
1 ≤ nums[i] ≤ 1000

Visualization

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Asked in

F Facebook 25 G Google 20

The key insight is that if we can make the array strictly increasing by removing exactly one element, there can be at most one violation point. The optimized approach scans once to count violations and validates if removal fixes the sequence. Time: O(n), Space: O(1)

Common Approaches

✓ Brute Force - Try Removing Each Element

⏱️ Time: O(n²) Space: O(n)

For each position in the array, create a new array without that element and check if the resulting array is strictly increasing. If any removal works, return true.

Single Pass - Count Violations

⏱️ Time: O(n) Space: O(1)

Scan the array once to find positions where the strictly increasing property is violated. If there are more than 2 violations, it's impossible. Otherwise, check if removing one element can fix all violations.

Brute Force - Try Removing Each Element — Algorithm Steps

For each index i from 0 to n-1
Create new array without element at index i
Check if new array is strictly increasing
If any removal works, return true

Visualization

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Step-by-Step Walkthrough

Original Array

Start with [2,3,1,2] - not strictly increasing

Try Removals

Remove each element and test remaining array

Found Solution

Removing index 2 gives [2,3,2] - still not working, but removing index 3 gives [2,3,1] - still not working, removing index 0 gives [3,1,2] - not working, removing index 1 gives [2,1,2] - not working. Actually removing index 2 gives [2,3,2] which is not strictly increasing either.

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

bool isStrictlyIncreasing(int* arr, int len) {
    for (int i = 1; i < len; i++) {
        if (arr[i] <= arr[i-1]) {
            return false;
        }
    }
    return true;
}

bool solution(int* nums, int n) {
    // Try removing each element
    for (int i = 0; i < n; i++) {
        // Create array without element at index i
        int* temp = (int*)malloc((n-1) * sizeof(int));
        int idx = 0;
        for (int j = 0; j < n; j++) {
            if (j != i) {
                temp[idx++] = nums[j];
            }
        }
        
        if (isStrictlyIncreasing(temp, n-1)) {
            free(temp);
            return true;
        }
        free(temp);
    }
    
    return false;
}

int main() {
    char line[10000];
    fgets(line, sizeof(line), stdin);
    line[strcspn(line, "\n")] = 0;
    
    // Simple JSON array parsing
    int nums[1000];
    int n = 0;
    char* token = strtok(line + 1, ",]");
    while (token != NULL) {
        nums[n++] = atoi(token);
        token = strtok(NULL, ",]");
    }
    
    bool result = solution(nums, n);
    printf(result ? "true\n" : "false\n");
    
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n²)

For each of n elements, we check if remaining n-1 elements form increasing sequence

✓ Linear Growth

Space Complexity

O(n)

Creating temporary arrays of size n-1 for each removal attempt

✓ Linear Space

23.4K Views

Medium Frequency

~15 min Avg. Time

890 Likes

Ln 1, Col 1

Smart Actions

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Input & Output

Constraints

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Related Problems

Common Approaches

Brute Force - Try Removing Each Element — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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