JavaScript 寻找数组中的第N大的元素
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<title>寻找数组中第K大的元素</title>
</head>
<body>
<h3>寻找数组中第K大的元素</h3>
<script>
// 冒泡排序法
function bubblingQueryArrIndex(arr,index) {
if (arr.length == 0) {
return;
}
if (index > arr.length - 1 || index - 1 < 0) {
return;
}
//冒泡排序
for (let i = 0; i < arr.length - 1; i ++ ) {
var flag = 0
for (let j = 0; j < arr.length - i - 1; j++) {
if (arr[j] < arr[j + 1]) {
var temp = arr[j + 1];
arr[j + 1] = arr[j];
arr[j] = temp;
flag = 1;
}
}
if (flag == 0) {
break;
}
}
console.log(arr);
return arr[index - 1];
}
console.log(bubblingQueryArrIndex([2,6,8,1,9,45,3],1));
//选择排序法
function chooseQueryArrIndex(arr,index) {
if (arr.length == 0) {
return;
}
if (index > arr.length - 1 || index - 1 < 0) {
return;
}
for (let i = 0; i < arr.length; i ++) {
for (let j = i + 1; j < arr.length; j ++) {
if (arr[i] < arr[j]) {
var temp = arr[j];
arr[j] = arr[i];
arr[i] = temp;
}
}
}
console.log(arr);
return arr[index - 1];
}
console.log(chooseQueryArrIndex([1,4,6,8,9,12,34,56,78],3));
//插入排序法 解决
function insertQueryArrIndex(arr,index) {
if (arr.length == 0) {
return;
}
if (index > arr.length - 1 || index - 1 < 0) {
return;
}
for (let i = 1; i < arr.length; i ++) {
var current = arr[i];
var preIndex = i - 1;
while (preIndex >= 0 && arr[preIndex] < current) {
arr[preIndex + 1] = arr[preIndex];
preIndex --;
}
arr[preIndex + 1] = current;
}
console.log(arr);
return arr[index - 1];
}
console.log(insertQueryArrIndex([1,4,6,8,9,12,34,56,78],3));
//二分插入排序
function binaryInsertQueryIndex(arr,index) {
if (arr.length == 0) {
return;
}
if (index > arr.length - 1 || index - 1 < 0) {
return;
}
for (let i = 1; i < arr.length; i ++) {
var current = arr[i];
var left = 0;
var right = i - 1;
while (left <= right) {
var mid = parseInt((left + right) / 2);
if (arr[mid] < current) {
right = mid - 1;
}else {
left = mid + 1;
}
}
for (let j = i - 1; j >= left; j--) {
arr[j + 1] = arr[j];
}
arr[left] = current;
}
console.log(arr);
return arr[index - 1];
}
console.log(binaryInsertQueryIndex([1,4,6,8,9,12,34,56,78],3));
//简化排序 只排前Index的数组
function mySort(arr,index) {
if (arr.length == 0) {
return;
}
if (index > arr.length - 1 || index - 1 < 0) {
return;
}
for (let i = 0; i < arr.length; i ++) {
if (i < index) { //排序 这里采用选择排序法
for (let j = i + 1; j < index; j ++) {
if (arr[i] < arr[j]) {
var temp = arr[j]
arr[j] = arr[i];
arr[i] = temp;
}
}
}else {
if (arr[i] > arr[index - 1]) {
arr[index - 1] = arr[i];
//再对前面的进行排序
for (let k = 0; k < index; k++) {
for (let s = k + 1; s < index; s++) {
if (arr[k] < arr[s]) {
var temp = arr[s];
arr[s] = arr[k];
arr[k] = temp;
}
}
}
}else {
continue;
}
}
}
console.log(arr);
return arr[index - 1];
}
console.log(mySort([1,4,6,8,89,9,12,34,56,78],3));
function myInsertSort(arr,index) {
if (arr.length == 0) {
return;
}
if (index > arr.length - 1 || index - 1 < 0) {
return;
}
var sortArr = [];
for (let i = 0; i < arr.length; i ++) {
var temp = arr[i];
if (i == 0) {
sortArr[i] = temp;
}
if (i < index) {
sortArr[i] = temp;
//排序
var preIndex = i - 1;
var current = sortArr[i];
while (preIndex >= 0 && sortArr[preIndex] < current) {
sortArr[preIndex + 1] = sortArr[preIndex];
preIndex --;
}
sortArr[preIndex + 1] = current;
}else {
if (temp > sortArr[index - 1]) {
sortArr[index - 1] = temp;
//排序
var preIndex = index - 1 - 1;
var current = sortArr[index - 1];
while (preIndex >= 0 && sortArr[preIndex] < current) {
sortArr[preIndex + 1] = sortArr[preIndex];
preIndex --;
}
sortArr[preIndex + 1] = current;
}else {
continue;
}
}
}
console.log(sortArr);
return sortArr[index - 1];
}
console.log(myInsertSort([1,4,6,8,89,9,12,34,56,78],3));
</script>
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后面应该还有更加简洁的算法 以后会补充
