js:数据结构笔记13--检索算法

顺序查找：也称线性查找，暴力查找的一种

• 基本格式：

var nums = [];

for(var i = 0; i < 10; ++i) {

    nums[i] = Math.floor(Math.random() * 101);

}



function seqSearch(arr,data) {

    for(var i = 0; i < arr.length; ++i) {

        if(arr[i] === data) {

            return i;

        }

    }

    return -1;

}

seqSearch(nums,45);

View Code

 //效率比Array.indexof()低；

• 查找最值：

function findMin(arr) {

    var min = arr[0];

    for(var i = 1; i < arr.length; ++i) {      //这里从第二个开始查找

        if(arr[i] < min) {                //arr[i] > max

            min = arr[i];

        }

    }

    return min;

}

View Code

• 自组织数据：经过多次查找之后，查找最频繁的元素会从原来的位置移动到数据集的起始位置

var nums = [0,45,101,12,5,12,78,45,5];



function seqSearch(arr,data) {

	for(var i = 0; i < arr.length; ++i) {

		if(arr[i] === data) {

			if( i > 0) {

				swap(arr,i,i-1);   //swap(arr,i,0);

				//console.log(arr);

			}

			return true;

		}

	}

	return false;

}



function swap(arr,index,index1) {

	temp = arr[index];

	arr[index] = arr[index1];

	arr[index1] = temp;

}



for(var i = 0; i < 4; ++i) {

	seqSearch(nums,5);

}

-----------------------------

[0, 45, 101, 5, 12, 12, 78, 45, 5] 
[0, 45, 5, 101, 12, 12, 78, 45, 5] 
[0, 5, 45, 101, 12, 12, 78, 45, 5] 
[5, 0, 45, 101, 12, 12, 78, 45, 5]

二分查找：如果数据是有序的，二分查找比顺序查找算法更高效；

var nums = [0,5,46,85,102,212,503];  //必须先排序好



function binSearch(arr,data) {

	var upperBound = arr.length - 1;

	    lowerBound = 0;

	while(lowerBound <= upperBound) {

		var mid = Math.floor((upperBound + lowerBound) / 2);

		if(arr[mid] < data) {

			lowerBound = mid + 1;

		} else if(arr[mid] > data) {

			upperBound = mid - 1;

		} else {

			return mid;

		}

	}

	return -1;

}



console.log(binSearch(nums,46));

• 计算次数：

function count(arr,data) {

	var count = 0,

		position = binSearch(arr,data);

		if(position > -1) {

			++count;

			for(var i = position-1; i > 0; --i) {

				if(arr[i] === data) {

					++count;

				} else {

					break;

				}

			}

			for(var i = position + 1; i < arr.length; ++i) {

				if(arr[i] === data) {

					++count;

				} else {

					break;

				}

			}

		}

		return count;

}



console.log(count(nums,5));