4. Median of Two Sorted Arrays

两个有序数组的中位数，相当于寻找两个数组第k大的值，利用二分法进行查找，确定之后改变k的值与起始索引。

合并两个有序数组类似解法

• Runtime: 120 ms, faster than 96.49%
• Memory Usage: 41.6 MB, less than 86.12%

var findMedianSortedArrays = function(nums1, nums2) {
    let len1 = nums1.length
    let len2 = nums2.length
    let len = len1 + len2
    if(len % 2 === 1) {
        return findKthDouble(nums1, nums2, (len + 1 ) / 2)
    } else {
        return (findKthDouble(nums1, nums2, len / 2) + findKthDouble(nums1, nums2, len / 2 + 1)) / 2
    }
};

var findKthDouble = function(nums1, nums2, k){
    let len1 = nums1.length
    let len2 = nums2.length
    let index1 = 0
    let index2 = 0
   
    while (true) {
        if (index1 === len1) {
            return nums2[index2 + k - 1]
        }
        if (index2 === len2) {
            return nums1[index1 + k - 1]
        }
        if(k === 1) {
            return Math.min(nums1[index1], nums2[index2])
        }
        let half = Math.floor(k / 2)
        let newIndex1 = Math.min(index1 + half, len1) - 1
        let newIndex2 = Math.min(index2 + half, len2) - 1
        let flag1 = nums1[newIndex1]
        let flag2 = nums2[newIndex2]
        if(flag1 <= flag2) {
            k -= (newIndex1 - index1 + 1)
            index1 = newIndex1 + 1
        } else if (flag1 > flag2) {
            k -= (newIndex2 - index2 + 1)
            index2 = newIndex2 + 1
        }
    }
}