769. Max Chunks To Make Sorted

Method 1

You are given an integer array arr of length n that represents a permutation of the integers in the range [0, n - 1].
We split arr into some number of chunks (i.e., partitions), and individually sort each chunk. After concatenating them, the result should equal the sorted array.
Return the largest number of chunks we can make to sort the array.

Example 1

Input: arr = [4,3,2,1,0]
Output: 1
Explanation:
Splitting into two or more chunks will not return the required result.
For example, splitting into [4, 3], [2, 1, 0] will result in [3, 4, 0, 1, 2], which isn't sorted.

Example 2

Input: arr = [1,0,2,3,4]
Output: 4
Explanation:
We can split into two chunks, such as [1, 0], [2, 3, 4].
However, splitting into [1, 0], [2], [3], [4] is the highest number of chunks possible.

Method 1

【O(n) time | O(k) space】

package Leetcode.Array;

/**
 * @author zhengxingxing
 * @date 2024/12/19
 */
public class MaxChunksToMakeSorted {
    public static int maxChunksToSorted(int[] arr) {
        int chunks = 0;      // Counter for number of valid chunks
        int currentMax = 0;  // Tracks maximum value seen so far

        // Iterate through the array
        // Key insight: if the maximum value seen equals current index,
        // all numbers before this position will be smaller and can form a chunk
        for (int i = 0; i < arr.length; i++) {
            currentMax = Math.max(currentMax, arr[i]);

            // If currentMax equals current index, we can form a valid chunk
            // Because all numbers in current chunk will be in their correct positions after sorting
            if(currentMax == i){
                chunks++;
            }
        }
        return chunks;
    }
    public static void main(String[] args) {
        // Test Case 1: Array that can only be split into 1 chunk
        int[] arr1 = {4,3,2,1,0};
        System.out.println("Test Case 1:");
        System.out.println("Input: " + java.util.Arrays.toString(arr1));
        System.out.println("Output: " + maxChunksToSorted(arr1));
        System.out.println("Expected: 1");
        System.out.println();

        // Test Case 2: Array that can be split into 4 chunks
        int[] arr2 = {1,0,2,3,4};
        System.out.println("Test Case 2:");
        System.out.println("Input: " + java.util.Arrays.toString(arr2));
        System.out.println("Output: " + maxChunksToSorted(arr2));
        System.out.println("Expected: 4");
        System.out.println();

        // Test Case 3: Already sorted array (maximum possible chunks)
        int[] arr3 = {0,1,2,3,4};
        System.out.println("Test Case 3:");
        System.out.println("Input: " + java.util.Arrays.toString(arr3));
        System.out.println("Output: " + maxChunksToSorted(arr3));
        System.out.println("Expected: 5");
    }
}

Method 1

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