面试10大算法题汇总-字符串和数组7

标签：面试   java   算法   二分查找   

14.实现strStr()：搜索一个字符串在另一个字符串中的第一次出现的位置

例：

#include <stdio.h>
#include <string.h>

int main ()
{
  char str[] ="This is a simple string";
  char * pch;
  pch = strstr (str,"simple");
  cout<<(*pch)<<endl;
  return 0;
}

输出：s

这里主要要考虑一下特殊情况。

Code：

public class test {
	public static String strStr(String origin, String needle) {
		int originLen = origin.length();
		int needleLen = needle.length();

		if (needleLen == originLen && originLen == 0)
			return "";
		if (needleLen == 0)
			return origin;

		for (int i = 0; i < originLen; ++i) {
			if (originLen - i + 1 < needleLen)
				return null;

			int k = i;
			int j = 0;

			while (j < needleLen && k < originLen
					&& needle.charAt(j) == origin.charAt(i)) {
				++j;
				++k;
				if (j == needleLen)
					return origin.substring(i);
			}
		}
		return null;
	}

	public static void main(String[] args) {
		int[] a = { 2, 7, 11, 23 };
	}
}

16.寻找插入位置：给定一个有序数组和一个目标值，若该值在数组中存在，则返回其index，否则返回其应该插入的位置。

例：

[1,3,5,6], 5 -> 2

[1,3,5,6], 2 -> 1

[1,3,5,6], 7 -> 4

[1,3,5,6], 0 -> 0

解法一：遍历

Code：

public class test {
	public static int arrPos(int[] A, int target) {
		if (A == null)
			return 0;

		if (target <= A[0])
			return 0;

		for (int i = 0; i < A.length - 1; i++) {
			if (target > A[i] && target <= A[i + 1]) {
				return i + 1;
			}
		}

		return A.length;
	}

	public static void main(String[] args) {
		int[] a = { 2, 7, 11, 23 };
		System.out.println(arrPos(a, 223));
	}
}

解法二：二分查找

Code：

public class test {
	public static int arrPos(int[] A, int target) {
		if (A == null || A.length == 0)
			return 0;

		return searchInsert(A, target, 0, A.length - 1);
	}

	public static int searchInsert(int[] A, int target, int start, int end) {
		int mid = (start + end) / 2;

		if (target == A[mid])
			return mid;
		else if (target < A[mid])
			return start < mid ? searchInsert(A, target, start, mid - 1)
					: start;
		else
			return end > mid ? searchInsert(A, target, mid + 1, end)
					: (end + 1);
	}

	public static void main(String[] args) {
		int[] a = { 2, 7, 11, 23 };
		System.out.println(arrPos(a, 223));
	}
}

面试10大算法题汇总-字符串和数组7

标签：面试   java   算法   二分查找   

原文地址：http://blog.csdn.net/miaoyunzexiaobao/article/details/44171361