经典的二分法

Find any position of a target number in a sorted array. Return -1 if target does not exist.

Example

Given [1, 2, 2, 4, 5, 5].

For target = 2, return 1 or 2.

For target = 5, return 4 or 5.

For target = 6, return -1.

二分法模板:

start + 1 < end

start + (end - start) / 2

a[mid] == , < , >

a[start], a[end] ? target

public class Solution {
/**
* @param nums: An integer array sorted in ascending order
* @param target: An integer
* @return an integer
*/
public int findPosition(int[] nums, int target) {
// Write your code here
if (nums == null || nums.length == 0) {
return -1;
}
int start = 0;
int end = nums.length - 1;
while (start + 1 < end) {
int mid = start + (end - start) / 2;
if (nums[mid] == target) {
return mid;
} else if (nums[mid] < target) {
start = mid;
} else {
end = mid;
}
}
if (nums[start] == target) {
return start;
}
if (nums[end] == target) {
return end;
}
return -1;
}
}