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package class_2022_07_4_week;
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// 一个数组如果满足 :
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// 升降升降升降... 或者 降升降升...都是满足的
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// 给定一个数组，
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// 1，看有几种方法能够剔除一个元素，达成上述的要求
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// 2，数组天然符合要求返回0
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// 3，剔除1个元素达成不了要求，返回-1，
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// 比如：
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// 给定[3, 4, 5, 3, 7]，返回3
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// 移除0元素，4 5 3 7 符合
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// 移除1元素，3 5 3 7 符合
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// 移除2元素，3 4 3 7 符合
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// 再比如：给定[1, 2, 3, 4] 返回-1
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// 因为达成不了要求
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public class Code01_WaysWiggle {
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// 暴力方法
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// 为了验证
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public static int ways1(int[] arr) {
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if (isWiggle(arr, -1)) {
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return 0;
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}
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int ans = 0;
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for (int i = 0; i < arr.length; i++) {
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if (isWiggle(arr, i)) {
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ans++;
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}
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}
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return ans == 0 ? -1 : ans;
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}
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public static boolean isWiggle(int[] arr, int removeIndex) {
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boolean ans = true;
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// 升
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boolean request = true;
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for (int i = 1; i < arr.length; i++) {
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if (i == removeIndex) {
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continue;
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}
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if (i - 1 == removeIndex && removeIndex == 0) {
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continue;
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}
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int last = i - 1 == removeIndex ? (i - 2) : (i - 1);
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if (request) {
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if (arr[last] >= arr[i]) {
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ans = false;
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break;
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}
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} else {
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if (arr[last] <= arr[i]) {
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ans = false;
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break;
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}
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}
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request = !request;
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}
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if (ans) {
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return true;
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}
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ans = true;
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// 降
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request = false;
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for (int i = 1; i < arr.length; i++) {
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if (i == removeIndex) {
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continue;
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}
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if (i - 1 == removeIndex && removeIndex == 0) {
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continue;
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}
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int last = i - 1 == removeIndex ? (i - 2) : (i - 1);
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if (request) {
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if (arr[last] >= arr[i]) {
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ans = false;
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break;
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}
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} else {
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if (arr[last] <= arr[i]) {
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ans = false;
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break;
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}
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}
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request = !request;
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}
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return ans;
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}
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// 时间复杂度O(N)
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public static int ways2(int[] arr) {
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if (arr == null || arr.length < 2) {
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return 0;
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}
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int n = arr.length;
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boolean[] up = new boolean[n];
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boolean[] down = new boolean[n];
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up[n - 1] = true;
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down[n - 1] = true;
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for (int i = n - 2; i >= 0; i--) {
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up[i] = arr[i] < arr[i + 1] && down[i + 1];
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down[i] = arr[i] > arr[i + 1] && up[i + 1];
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}
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if (up[0] || down[0]) {
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return 0;
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}
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int ans = (up[1] || down[1]) ? 1 : 0;
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boolean leftUp = true;
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boolean leftDown = true;
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boolean tmp;
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for (int i = 1, l = 0, r = 2; i < n - 1; i++, l++, r++) {
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ans += (arr[l] > arr[r] && up[r] && leftDown) || (arr[l] < arr[r] && down[r] && leftUp) ? 1 : 0;
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tmp = leftUp;
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leftUp = arr[l] > arr[i] && leftDown;
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leftDown = arr[l] < arr[i] && tmp;
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}
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ans += leftUp || leftDown ? 1 : 0;
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return ans == 0 ? -1 : ans;
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}
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// 为了验证
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public static int[] randomArray(int len, int maxValue) {
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int[] ans = new int[len];
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for (int i = 0; i < len; i++) {
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ans[i] = (int) (Math.random() * maxValue) + 1;
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}
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return ans;
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}
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// 为了验证
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public static void main(String[] args) {
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int maxLen = 10;
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int maxValue = 100;
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int testTime = 30000;
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System.out.println("测试开始");
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for (int i = 0; i < testTime; i++) {
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int len = (int) (Math.random() * maxLen) + 1;
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int[] arr = randomArray(len, maxValue);
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int ans1 = ways1(arr);
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int ans2 = ways2(arr);
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if (ans1 != ans2) {
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System.out.println("出错了！");
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}
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}
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System.out.println("测试结束");
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}
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}
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