algo/javascript/12_sorts/KthNum.js
2019-03-27 19:17:59 +08:00

41 lines
696 B
JavaScript

/**
* 第k大的数
* @param {array} arr
* @param {number} k
*/
function kthNum(arr, k) {
const len = arr.length;
if (k > len) {
return -1;
}
let p = partition(arr, 0, len - 1);
while (p + 1 !== k) {
if (p + 1 > k) {
p = partition(arr, 0, p - 1);
} else {
p = partition(arr, p + 1, len - 1);
}
}
return arr[p];
}
function partition(arr, start, end) {
let i = start;
let pivot = arr[end];
for (let j = start; j < end; j++) {
if (arr[j] > pivot) {
swap(arr, i, j);
i += 1;
}
}
swap(arr, i, end);
return i;
}
function swap(arr, i, j) {
if (i === j) return;
let tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}