LeetCode 4 题解

nums1 = [1, 3]
nums2 = [2]

nums1 = [1, 2]
nums2 = [3, 4]

class Solution {
    public double findMedianSortedArrays(int[] nums1, int[] nums2) {

        int len = nums1.length + nums2.length;
        int[] a = new int[len];
        int k = 0;
        for (int i = 0; i < nums1.length; i++) {
            a[k++] = nums1[i];
        }
        for (int i = 0; i < nums2.length; i++) {
            a[k++] = nums2[i];
        }
        mergesort(a, 0, len - 1);

        if (len % 2 == 1) {
            return (double) a[len / 2];
        } else {
            return (double) (a[len / 2 - 1] + a[len / 2]) / 2;
        }
    }

     /**
     * @param a
     * @param i
     * @param length
     */
    private void mergesort(int[] a, int start, int end) {
        if (end > start) {
            int mid = (start + end) / 2;
            mergesort(a, start, mid);
            mergesort(a, mid + 1, end);
            merge(a, start, mid, end);
        }
    }

    /**
     * @param a
     * @param start
     * @param i
     * @param end
     */
    private void merge(int[] a, int start, int mid, int end) {
        // 二分 start -mid 是一个，mid -end 是一个
        int[] b = new int[end + 1];
        int k = start;
        int i, j;
        for (i = start, j = mid + 1; i <= mid && j <= end; k++) {
            if (a[i] < a[j]) {
                b[k] = a[i++];
            } else {
                b[k] = a[j++];
            }
        }
        while (j <= end) {
            b[k++] = a[j++];
        }

        while (i <= mid) {
            b[k++] = a[i++];
        }

        for (int l = start; l <= end; l++) {
            a[start++] = b[l];
        }
    }
}