Three Increasing Elements in an Array

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本文介绍了一种算法，用于在整数数组中找到三个互不相同的索引，使得这三个索引对应的元素值依次递增。算法通过迭代数组并维护当前最小值和次小值来实现这一目标。

Problem: Given an array of integers A, please find three indexes i, j, k, such that i<j<k and A[i]<A[j]<A[k].

参考：http://codercareer.blogspot.com/2013/02/no-42-three-increasing-elements-in-array.html

数组问题画张图总是比较清晰。i和j连成的线要尽量接近X轴，这样K可选的范围就最大。

/* Copyleft: Ming Lin <minggr@gmail.com> */

#include <stdio.h>

void find_three_increase_elements(int data[], int n)
{
	int m;
	int i, j, k;
	int t;

	i = j = k = -1;
	t = -1;

	for (m = 0; m < n; m++) {
		if (i == -1)
			i = m;
		else {
			if (j == -1) {
				if (data[m] <= data[i])
					i = m;
				else
					j = m;
			} else {
				/* 3 cases */
				if (data[m] > data[j]) {
					k = m;
					printf("i=%d, j=%d, k=%d\n", i, j, k);
					return;
				} else if (data[m] < data[j]) {
					if (t != -1) {
						i = t;
						j = m;
						t = -1;
					} else {
						t = m;
					}
				} else if (data[m] > data[i] && data[m] < data[j]) {
					j = m;
				}
			}
		}
	}
}

int main()
{
	int data[] =  {3, 2, 5, 1, 4, 7, 9, 6, 8};
	int n = 9;

	find_three_increase_elements(data, n);	

	return 0;
}