Leecode刷题（二）

4.寻找两个正序数组的中位数

package topinterviewquestions;

public class Problem_0004_MedianOfTwoSortedArrays {

	public static double findMedianSortedArrays(int[] nums1, int[] nums2) {
		int size = nums1.length + nums2.length;
		boolean even = (size & 1) == 0;
		if (nums1.length != 0 && nums2.length != 0) {
			if (even) {
				return (double) (findKthNum(nums1, nums2, size / 2) + findKthNum(nums1, nums2, size / 2 + 1)) / 2D;
			} else {
				return findKthNum(nums1, nums2, size / 2 + 1);
			}
		} else if (nums1.length != 0) {
			if (even) {
				return (double) (nums1[(size - 1) / 2] + nums1[size / 2]) / 2;
			} else {
				return nums1[size / 2];
			}
		} else if (nums2.length != 0) {
			if (even) {
				return (double) (nums2[(size - 1) / 2] + nums2[size / 2]) / 2;
			} else {
				return nums2[size / 2];
			}
		} else {
			return 0;
		}
	}

	public static int findKthNum(int[] arr1, int[] arr2, int kth) {
		int[] longs = arr1.length >= arr2.length ? arr1 : arr2;
		int[] shorts = arr1.length < arr2.length ? arr1 : arr2;
		int l = longs.length;
		int s = shorts.length;
		if (kth <= s) {
			return getUpMedian(shorts, 0, kth - 1, longs, 0, kth - 1);
		}
		if (kth > l) {
			if (shorts[kth - l - 1] >= longs[l - 1]) {
				return shorts[kth - l - 1];
			}
			if (longs[kth - s - 1] >= shorts[s - 1]) {
				return longs[kth - s - 1];
			}
			return getUpMedian(shorts, kth - l, s - 1, longs, kth - s, l - 1);
		}
		// 第2段
		if (longs[kth - s - 1] >= shorts[s - 1]) {
			return longs[kth - s - 1];
		}
		return getUpMedian(shorts, 0, s - 1, longs, kth - s, kth - 1);
	}

	public static int getUpMedian(int[] A, int s1, int e1, int[] B, int s2, int e2) {
		int mid1 = 0;
		int mid2 = 0;
		while (s1 < e1) {
			mid1 = (s1 + e1) / 2;
			mid2 = (s2 + e2) / 2;
			if (A[mid1] == B[mid2]) {
				return A[mid1];
			}
			if (((e1 - s1 + 1) & 1) == 1) { // 奇数长度
				if (A[mid1] > B[mid2]) {
					if (B[mid2] >= A[mid1 - 1]) {
						return B[mid2];
					}
					e1 = mid1 - 1;
					s2 = mid2 + 1;
				} else { // A[mid1] < B[mid2]
					if (A[mid1] >= B[mid2 - 1]) {
						return A[mid1];
					}
					e2 = mid2 - 1;
					s1 = mid1 + 1;
				}
			} else { // 偶数长度
				if (A[mid1] > B[mid2]) {
					e1 = mid1;
					s2 = mid2 + 1;
				} else {
					e2 = mid2;
					s1 = mid1 + 1;
				}
			}
		}
		return Math.min(A[s1], B[s2]);
	}

}

5. 最长回文子串

package topinterviewquestions;

public class Problem_0005_LongestPalindromicSubstring {

	public static String longestPalindrome(String str) {
		if (str == null || str.length() == 0) {
			return "";
		}
		char[] charArr = manacherString(str);
		int[] pArr = new int[charArr.length];
		int index = -1;
		int pR = -1;
		int max = Integer.MIN_VALUE;
		int mid = 0;
		for (int i = 0; i != charArr.length; i++) {
			pArr[i] = pR > i ? Math.min(pArr[2 * index - i], pR - i) : 1;
			while (i + pArr[i] < charArr.length && i - pArr[i] > -1) {
				if (charArr[i + pArr[i]] == charArr[i - pArr[i]])
					pArr[i]++;
				else {
					break;
				}
			}
			if (i + pArr[i] > pR) {
				pR = i + pArr[i];
				index = i;
			}
			if (max < pArr[i]) {
				max = pArr[i];
				mid = i;
			}
		}
		mid = (mid - 1) / 2;
		max = max - 1;
		return str.substring((max & 1) == 0 ? mid - (max / 2) + 1 : mid - (max / 2), mid + (max / 2) + 1);
	}

	public static char[] manacherString(String str) {
		char[] charArr = str.toCharArray();
		char[] res = new char[str.length() * 2 + 1];
		int index = 0;
		for (int i = 0; i != res.length; i++) {
			res[i] = (i & 1) == 0 ? '#' : charArr[index++];
		}
		return res;
	}

}

7. 整数反转

package topinterviewquestions;

public class Problem_0007_ReverseInteger {

	public static int reverse(int x) {
		boolean neg = ((x >>> 31) & 1) == 1;
		x = neg ? x : -x;
		int m = Integer.MIN_VALUE / 10;
		int o = Integer.MIN_VALUE % 10;
		int res = 0;
		while (x != 0) {
			if (res < m || (res == m && x % 10 < o)) {
				return 0;
			}
			res = res * 10 + x % 10;
			x /= 10;
		}
		return neg ? res : Math.abs(res);
	}

}