package class25;

import java.util.Stack;

public class Code02_AllTimesMinToMax {

	public static int max1(int[] arr) {
		int max = Integer.MIN_VALUE;
		for (int i = 0; i < arr.length; i++) {
			for (int j = i; j < arr.length; j++) {
				int minNum = Integer.MAX_VALUE;
				int sum = 0;
				for (int k = i; k <= j; k++) {
					sum += arr[k];
					minNum = Math.min(minNum, arr[k]);
				}
				max = Math.max(max, minNum * sum);
			}
		}
		return max;
	}

	public static int max2(int[] arr) {
		int size = arr.length;
		int[] sums = new int[size];
		sums[0] = arr[0];
		for (int i = 1; i < size; i++) {
			sums[i] = sums[i - 1] + arr[i];
		}
		int max = Integer.MIN_VALUE;
		Stack<Integer> stack = new Stack<Integer>();
		for (int i = 0; i < size; i++) {
			while (!stack.isEmpty() && arr[stack.peek()] >= arr[i]) {
				int j = stack.pop();
				max = Math.max(max, (stack.isEmpty() ? sums[i - 1] : (sums[i - 1] - sums[stack.peek()])) * arr[j]);
			}
			stack.push(i);
		}
		while (!stack.isEmpty()) {
			int j = stack.pop();
			max = Math.max(max, (stack.isEmpty() ? sums[size - 1] : (sums[size - 1] - sums[stack.peek()])) * arr[j]);
		}
		return max;
	}

	public static int[] gerenareRondomArray() {
		int[] arr = new int[(int) (Math.random() * 20) + 10];
		for (int i = 0; i < arr.length; i++) {
			arr[i] = (int) (Math.random() * 101);
		}
		return arr;
	}

	public static void main(String[] args) {
		int testTimes = 2000000;
		System.out.println("test begin");
		for (int i = 0; i < testTimes; i++) {
			int[] arr = gerenareRondomArray();
			if (max1(arr) != max2(arr)) {
				System.out.println("FUCK!");
				break;
			}
		}
		System.out.println("test finish");
	}

	// 本题可以在leetcode上找到原题
	// 测试链接 : https://leetcode.com/problems/maximum-subarray-min-product/
	// 注意测试题目数量大，要取模，但是思路和课上讲的是完全一样的
	// 注意溢出的处理即可，也就是用long类型来表示累加和
	// 还有优化就是，你可以用自己手写的数组栈，来替代系统实现的栈，也会快很多
	public static int maxSumMinProduct(int[] arr) {
		int size = arr.length;
		long[] sums = new long[size];
		sums[0] = arr[0];
		for (int i = 1; i < size; i++) {
			sums[i] = sums[i - 1] + arr[i];
		}
		long max = Long.MIN_VALUE;
		int[] stack = new int[size];
		int stackSize = 0;
		for (int i = 0; i < size; i++) {
			while (stackSize != 0 && arr[stack[stackSize - 1]] >= arr[i]) {
				int j = stack[--stackSize];
				max = Math.max(max,
						(stackSize == 0 ? sums[i - 1] : (sums[i - 1] - sums[stack[stackSize - 1]])) * arr[j]);
			}
			stack[stackSize++] = i;
		}
		while (stackSize != 0) {
			int j = stack[--stackSize];
			max = Math.max(max,
					(stackSize == 0 ? sums[size - 1] : (sums[size - 1] - sums[stack[stackSize - 1]])) * arr[j]);
		}
		return (int) (max % 1000000007);
	}

}