kth largest element in an array

找第k大，exch+partition+select：

private void exch(int[] a, int i, int j) {
int t = a[i];
a[i] = a[j];
a[j] = t;
}

private int partition(int[] a, int lo, int hi) {
int i = lo, j = hi + 1;
int v = a[lo];
while (true) {
while (a[++i] > v && i != hi) ;
while (a[--j] < v && j != lo) ;
if (i >= j) break;
exch(a, i, j);
}
exch(a, lo, j);
return j;
}

public int findKthLargest(int[] nums, int k) {
int lo = 0, hi = nums.length - 1;
while (lo < hi) {
int j = partition(nums, lo, hi);
if (j + 1 == k) {
return nums[k - 1];
} else if (j + 1 > k) {
hi--;
} else {
lo++;
}
}
return nums[k - 1];
}