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package class_2022_03_3_week;
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// 来自bilibili
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// 现在有N条鱼，每条鱼的体积为Ai，从左到右排列，数组arr给出
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// 每一轮，左边的大鱼一定会吃掉右边比自己小的第一条鱼，
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// 并且每条鱼吃比自己小的鱼的事件是同时发生的。
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// 返回多少轮之后，鱼的数量会稳定
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// 注意：6 6 3 3
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// 第一轮过后 :
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// 对于两个6来说，右边比自己小的第一条鱼都是第1个3，所以只有这个3被吃掉，
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// 数组变成 : 6 6 3（第2个3）
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// 第二轮过后 : 6 6
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// 返回2
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public class Code05_EatFish {
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public static int minTurns1(int[] arr) {
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int ans = 0;
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for (;; ans++) {
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int[] rest = eatRest(arr);
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if (arr.length == rest.length) {
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break;
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}
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arr = rest;
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}
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return ans;
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}
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public static int[] eatRest(int[] arr) {
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if (arr.length == 0) {
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return new int[0];
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}
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int n = arr.length;
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boolean[] delete = new boolean[n];
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int len = n;
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for (int i = 0; i < n; i++) {
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for (int j = i + 1; j < n; j++) {
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if (arr[i] > arr[j]) {
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if (!delete[j]) {
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delete[j] = true;
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len--;
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}
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break;
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}
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}
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}
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int[] rest = new int[len];
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for (int i = 0, j = 0; i < n; i++) {
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if (!delete[i]) {
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rest[j++] = arr[i];
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}
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}
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return rest;
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}
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public static int minTurns2(int[] arr) {
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int n = arr.length;
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int[][] stack = new int[n][2];
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int stackSize = 0;
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int ans = 0;
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for (int i = n - 1; i >= 0; i--) {
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int curAns = 0;
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while (stackSize > 0 && stack[stackSize - 1][0] < arr[i]) {
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curAns = Math.max(curAns + 1, stack[--stackSize][1]);
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}
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stack[stackSize][0] = arr[i];
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stack[stackSize++][1] = curAns;
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ans = Math.max(ans, curAns);
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}
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return ans;
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}
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// 为了测试
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public static int[] randomArray(int n, int v) {
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int[] arr = new int[n];
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for (int i = 0; i < n; i++) {
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arr[i] = (int) (Math.random() * v);
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}
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return arr;
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}
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// 为了测试
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public static void main(String[] args) {
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int len = 50;
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int value = 20;
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int testTime = 20000;
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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 n = (int) (Math.random() * len) + 1;
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int[] arr = randomArray(n, value);
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int ans1 = minTurns1(arr);
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int ans2 = minTurns2(arr);
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if (ans1 != ans2) {
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System.out.println("出错了!");
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for (int num : arr) {
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System.out.print(num + " ");
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}
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System.out.println();
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System.out.println(ans1);
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System.out.println(ans2);
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break;
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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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