_88.java

package com.fishercoder.solutions;

/**Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.

 Note:
 You may assume that nums1 has enough space (size that is greater or equal to m + n)
 to hold additional elements from nums2. The number of elements initialized in nums1 and nums2 are m and n respectively.*/

public class _88 {

    //credit:https://discuss.leetcode.com/topic/2461/this-is-my-ac-code-may-help-you
    public static void merge_O1_space(int[] nums1, int m, int[] nums2, int n) {
        int i = m - 1;
        int j = n - 1;
        int k = m + n - 1;
        while (i >= 0 && j >= 0) {
            if (nums1[i] > nums2[j]) {
                nums1[k--] = nums1[i--];
            } else {
                nums1[k--] = nums2[j--];
            }
        }
        while (j >= 0) {
            nums1[k--] = nums2[j--];
        }
    }

    /**
     * I used O(m) extra space to create a temp array, but this could be optimized.
     */
    public static void merge(int[] nums1, int m, int[] nums2, int n) {
        int[] temp = new int[m];
        for (int i = 0; i < m; i++) {
            temp[i] = nums1[i];
        }
        for (int i = 0, j = 0, k = 0; i < m || j < n; ) {
            if (i == m) {
                for (; j < n; ) {
                    nums1[k++] = nums2[j++];
                }
                break;
            }
            if (j == n) {
                for (; i < m; ) {
                    nums1[k++] = temp[i++];
                }
                break;
            }

            if (temp[i] > nums2[j]) {
                nums1[k++] = nums2[j++];
            } else {
                nums1[k++] = temp[i++];
            }
        }
    }

    public static void main(String... args) {
//        int[] nums1 = new int[]{2,0};
//        int m = 1;
//        int[] nums2 = new int[]{1};
//        int n = 1;

        int[] nums1 = new int[]{4, 5, 6, 0, 0, 0};
        int m = 3;
        int[] nums2 = new int[]{1, 2, 3};
        int n = 3;
        merge(nums1, m, nums2, n);
    }
}