Trying to solve this Easy LeetCode question using two ptrs. Values for m & n should be constant, and I'm not decrementing the value for i anywhere else. Why is my for-loop not decrementing after i = 0? Any ideas? TIA!

class Solution {
public void merge(int[] nums1, int m, int[] nums2, int n) {
    //Start filling nums1[] from the end instead
    //Will run in O(m n) = nums1.length()
    int ptr1 = m-1, ptr2 = n-1;
    for(int i = m n-1; i > -1; i--){
        //System.out.println("i = "   i);
        //System.out.println("ptr1 = "   ptr1   "\tptr2 = "   ptr2);
        if(ptr2 < 0 || nums1[ptr1] > nums2[ptr2])
            nums1[i] = nums1[ptr1--];
        else
            nums1[i] = nums2[ptr2--];
        System.out.println("nums1["   i   "] = "   nums1[i]);
    }
}

}

CodePudding user response：

Your problem is not where you think it is.

The for loop correctly exits.

The output you show is from test case 1 (lines 1 to 6):

Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3

nums1[5] = 6
nums1[4] = 5
nums1[3] = 3
nums1[2] = 2
nums1[1] = 2
nums1[0] = 1

and from test case 2 (line 7):

Input: nums1 = [1], m = 1, nums2 = [], n = 0

nums1[0] = 1

and then your code fails for test case 3

Input: nums1 = [0], m = 0, nums2 = [1], n = 1

You can verify that the for loop correctly exits by adding a System.out.println("Done"); after the for loop.

CodePudding user response：

Try this:

public class Test {
public static void main(String[] args) {
    
    for (int i=6; i>-1; i--)
    {
        System.out.println(i);
    }
}

}