algorithm-class/体系学习班/class45/Code01_InsertS2MakeMostAlphabeticalOrder.java

package class45;

public class Code01_InsertS2MakeMostAlphabeticalOrder {

	// 暴力方法
	public static String right(String s1, String s2) {
		if (s1 == null || s1.length() == 0) {
			return s2;
		}
		if (s2 == null || s2.length() == 0) {
			return s1;
		}
		String p1 = s1 + s2;
		String p2 = s2 + s1;
		String ans = p1.compareTo(p2) > 0 ? p1 : p2;
		for (int end = 1; end < s1.length(); end++) {
			String cur = s1.substring(0, end) + s2 + s1.substring(end);
			if (cur.compareTo(ans) > 0) {
				ans = cur;
			}
		}
		return ans;
	}

	// 正式方法 O(N+M) + O(M^2)
	// N : s1长度
	// M : s2长度
	public static String maxCombine(String s1, String s2) {
		if (s1 == null || s1.length() == 0) {
			return s2;
		}
		if (s2 == null || s2.length() == 0) {
			return s1;
		}
		char[] str1 = s1.toCharArray();
		char[] str2 = s2.toCharArray();
		int N = str1.length;
		int M = str2.length;
		int min = str1[0];
		int max = str1[0];
		for (int i = 1; i < N; i++) {
			min = Math.min(min, str1[i]);
			max = Math.max(max, str1[i]);
		}
		for (int i = 0; i < M; i++) {
			min = Math.min(min, str2[i]);
			max = Math.max(max, str2[i]);
		}
		int[] all = new int[N + M + 1];
		int index = 0;
		for (int i = 0; i < N; i++) {
			all[index++] = str1[i] - min + 2;
		}
		all[index++] = 1;
		for (int i = 0; i < M; i++) {
			all[index++] = str2[i] - min + 2;
		}
		DC3 dc3 = new DC3(all, max - min + 2);
		int[] rank = dc3.rank;
		int comp = N + 1;
		for (int i = 0; i < N; i++) {
			if (rank[i] < rank[comp]) {
				int best = bestSplit(s1, s2, i);
				return s1.substring(0, best) + s2 + s1.substring(best);
			}
		}
		return s1 + s2;
	}

	public static int bestSplit(String s1, String s2, int first) {
		int N = s1.length();
		int M = s2.length();
		int end = N;
		for (int i = first, j = 0; i < N && j < M; i++, j++) {
			if (s1.charAt(i) < s2.charAt(j)) {
				end = i;
				break;
			}
		}
		String bestPrefix = s2;
		int bestSplit = first;
		for (int i = first + 1, j = M - 1; i <= end; i++, j--) {
			String curPrefix = s1.substring(first, i) + s2.substring(0, j);
			if (curPrefix.compareTo(bestPrefix) >= 0) {
				bestPrefix = curPrefix;
				bestSplit = i;
			}
		}
		return bestSplit;
	}

	public static class DC3 {

		public int[] sa;

		public int[] rank;

		public DC3(int[] nums, int max) {
			sa = sa(nums, max);
			rank = rank();
		}

		private int[] sa(int[] nums, int max) {
			int n = nums.length;
			int[] arr = new int[n + 3];
			for (int i = 0; i < n; i++) {
				arr[i] = nums[i];
			}
			return skew(arr, n, max);
		}

		private int[] skew(int[] nums, int n, int K) {
			int n0 = (n + 2) / 3, n1 = (n + 1) / 3, n2 = n / 3, n02 = n0 + n2;
			int[] s12 = new int[n02 + 3], sa12 = new int[n02 + 3];
			for (int i = 0, j = 0; i < n + (n0 - n1); ++i) {
				if (0 != i % 3) {
					s12[j++] = i;
				}
			}
			radixPass(nums, s12, sa12, 2, n02, K);
			radixPass(nums, sa12, s12, 1, n02, K);
			radixPass(nums, s12, sa12, 0, n02, K);
			int name = 0, c0 = -1, c1 = -1, c2 = -1;
			for (int i = 0; i < n02; ++i) {
				if (c0 != nums[sa12[i]] || c1 != nums[sa12[i] + 1] || c2 != nums[sa12[i] + 2]) {
					name++;
					c0 = nums[sa12[i]];
					c1 = nums[sa12[i] + 1];
					c2 = nums[sa12[i] + 2];
				}
				if (1 == sa12[i] % 3) {
					s12[sa12[i] / 3] = name;
				} else {
					s12[sa12[i] / 3 + n0] = name;
				}
			}
			if (name < n02) {
				sa12 = skew(s12, n02, name);
				for (int i = 0; i < n02; i++) {
					s12[sa12[i]] = i + 1;
				}
			} else {
				for (int i = 0; i < n02; i++) {
					sa12[s12[i] - 1] = i;
				}
			}
			int[] s0 = new int[n0], sa0 = new int[n0];
			for (int i = 0, j = 0; i < n02; i++) {
				if (sa12[i] < n0) {
					s0[j++] = 3 * sa12[i];
				}
			}
			radixPass(nums, s0, sa0, 0, n0, K);
			int[] sa = new int[n];
			for (int p = 0, t = n0 - n1, k = 0; k < n; k++) {
				int i = sa12[t] < n0 ? sa12[t] * 3 + 1 : (sa12[t] - n0) * 3 + 2;
				int j = sa0[p];
				if (sa12[t] < n0 ? leq(nums[i], s12[sa12[t] + n0], nums[j], s12[j / 3])
						: leq(nums[i], nums[i + 1], s12[sa12[t] - n0 + 1], nums[j], nums[j + 1], s12[j / 3 + n0])) {
					sa[k] = i;
					t++;
					if (t == n02) {
						for (k++; p < n0; p++, k++) {
							sa[k] = sa0[p];
						}
					}
				} else {
					sa[k] = j;
					p++;
					if (p == n0) {
						for (k++; t < n02; t++, k++) {
							sa[k] = sa12[t] < n0 ? sa12[t] * 3 + 1 : (sa12[t] - n0) * 3 + 2;
						}
					}
				}
			}
			return sa;
		}

		private void radixPass(int[] nums, int[] input, int[] output, int offset, int n, int k) {
			int[] cnt = new int[k + 1];
			for (int i = 0; i < n; ++i) {
				cnt[nums[input[i] + offset]]++;
			}
			for (int i = 0, sum = 0; i < cnt.length; ++i) {
				int t = cnt[i];
				cnt[i] = sum;
				sum += t;
			}
			for (int i = 0; i < n; ++i) {
				output[cnt[nums[input[i] + offset]]++] = input[i];
			}
		}

		private boolean leq(int a1, int a2, int b1, int b2) {
			return a1 < b1 || (a1 == b1 && a2 <= b2);
		}

		private boolean leq(int a1, int a2, int a3, int b1, int b2, int b3) {
			return a1 < b1 || (a1 == b1 && leq(a2, a3, b2, b3));
		}

		private int[] rank() {
			int n = sa.length;
			int[] ans = new int[n];
			for (int i = 0; i < n; i++) {
				ans[sa[i]] = i;
			}
			return ans;
		}

	}

	// for test
	public static String randomNumberString(int len, int range) {
		char[] str = new char[len];
		for (int i = 0; i < len; i++) {
			str[i] = (char) ((int) (Math.random() * range) + '0');
		}
		return String.valueOf(str);
	}

	// for test
	public static void main(String[] args) {
		int range = 10;
		int len = 50;
		int testTime = 100000;
		System.out.println("功能测试开始");
		for (int i = 0; i < testTime; i++) {
			int s1Len = (int) (Math.random() * len);
			int s2Len = (int) (Math.random() * len);
			String s1 = randomNumberString(s1Len, range);
			String s2 = randomNumberString(s2Len, range);
			String ans1 = right(s1, s2);
			String ans2 = maxCombine(s1, s2);
			if (!ans1.equals(ans2)) {
				System.out.println("Oops!");
				System.out.println(s1);
				System.out.println(s2);
				System.out.println(ans1);
				System.out.println(ans2);
				break;
			}
		}
		System.out.println("功能测试结束");

		System.out.println("==========");

		System.out.println("性能测试开始");
		int s1Len = 1000000;
		int s2Len = 500;
		String s1 = randomNumberString(s1Len, range);
		String s2 = randomNumberString(s2Len, range);
		long start = System.currentTimeMillis();
		maxCombine(s1, s2);
		long end = System.currentTimeMillis();
		System.out.println("运行时间 : " + (end - start) + " ms");
		System.out.println("性能测试结束");
	}

}