leetcode——4.寻找两个有序数组的中位数

class Solution:
    def findMedianSortedArrays(self, nums1, nums2) -> float:
        c=sorted(nums1+nums2)
        if len(c)%2==0:
            return (c[len(c)//2]+c[len(c)//2-1])/2
        else:
            return float(c[(len(c)-1)//2])

执行用时 :104 ms, 在所有 Python3 提交中击败了85.76%的用户

内存消耗 :14.1 MB, 在所有 Python3 提交中击败了5.28%的用户

                                                                                                 ——2019.10.7

 

---

public double findMedianSortedArrays(int[] nums1, int[] nums2) {
        //递归
        int n = nums1.length;
        int m = nums2.length;
        int left = (n+m+1) / 2;
        int right = (n+m+2) /2;
        return (getKth(nums1,0,n-1,nums2,0,m-1,left) + getKth(nums1,0,n-1,nums2,0,m-1,right)) * 0.5;
    }

    private double getKth(int[] nums1, int start1, int end1, int[] nums2, int start2, int end2, int k) {
        int len1 = end1 - start1 + 1;
        int len2 = end2 - start2 + 1;
        if(len1 > len2){    //让len1的长度小于len2，这样如果有数组空了，就能保证一定是len1
            return getKth(nums2,start2,end2,nums1,start1,end1 ,k);
        }
        if(len1 == 0){
            return nums2[start2 + k - 1];
        }
        if(k == 1){
            return Math.min(nums1[start1],nums2[start2]);
        }
        int i = start1 + Math.min(len1,k/2)-1;
        int j = start2 + Math.min(len2,k/2)-1;
        if(nums1[i] > nums2[j]){
            return getKth(nums1,start1,end1,nums2,j+1,end2,k-(j - start2 +1));
        }else{
            return getKth(nums1,i+1,end1,nums2,start2,end2,k-(i - start1 +1));
        }
    }

——2020.7.9

---

public double findMedianSortedArrays(int[] nums1, int[] nums2) {   //递归做法下午再做
        int n1 = nums1.length;
        int n2 = nums2.length;
        int len = n1+n2;
        if(len%2==1){
            int medIndex = len/2;
            return getKthElement(nums1,nums2,medIndex+1,0,0,n1,n2);
        }else{
            int medIndex1 = len/2-1,medIndex2 = len/2;
            double median1 = getKthElement(nums1,nums2,medIndex1+1,0,0,n1,n2);
            double median2 = getKthElement(nums1,nums2,medIndex2+1,0,0,n1,n2);
            return (median1+median2)/2.0;
        }
    }

    private int getKthElement(int[] nums1, int[] nums2, int k,int index1,int index2,int n1,int n2) {
        if(index1 == n1){
            return nums2[index2+k-1];
        }
        if(index2 == n2){
            return nums1[index1+k-1];
        }
        if(k == 1){
            return Math.min(nums1[index1],nums2[index2]);
        }

        int half = k/2;
        int newIndex1 = Math.min(index1+half,n1)-1;
        int newIndex2 = Math.min(index2+half,n2)-1;
        if(nums1[newIndex1]<=nums2[newIndex2]){
            k -= (newIndex1 - index1 +1);
            index1 = newIndex1 + 1;
            return getKthElement(nums1,nums2,k,index1,index2,n1,n2);
        }else{
            k -= (newIndex2 - index2 +1);
            index2 = newIndex2 + 1;
            return getKthElement(nums1,nums2,k,index1,index2,n1,n2);
        }
    }

递归。

    public double findMedianSortedArrays(int[] nums1, int[] nums2) {   //递归做法下午再做
        int n1 = nums1.length;
        int n2 = nums2.length;
        int len = n1+n2;
        if(len%2==1){
            int medIndex = len/2;
            double median = getKthElement(nums1,nums2,medIndex+1);
            return median;
        }else{
            int medIndex1 = len/2-1,medIndex2 = len/2;
            double median1 = getKthElement(nums1,nums2,medIndex1+1);
            double median2 = getKthElement(nums1,nums2,medIndex2+1);
            double median = (median1+median2)/2.0;
            return median;
        }
    }

    private int getKthElement(int[] nums1, int[] nums2, int k) {
        int n1 = nums1.length;
        int n2 = nums2.length;
        int index1 = 0,index2 = 0;
        while (true){
            if(index1 == n1){
                return nums2[index2+k-1];
            }
            if(index2 == n2){
                return nums1[index1+k-1];
            }
            if(k == 1){
                return Math.min(nums1[index1],nums2[index2]);
            }

            int half = k/2;
            int newIndex1 = Math.min(index1+half,n1)-1;
            int newIndex2 = Math.min(index2+half,n2)-1;
            if(nums1[newIndex1]<=nums2[newIndex2]){
                k -= (newIndex1 - index1 +1);
                index1 = newIndex1 + 1;
            }else{
                k -= (newIndex2 - index2 +1);
                index2 = newIndex2 + 1;
            }
        }
    }

——2020.8.31