misc

Author: MaskRay

find-k-pairs-with-smallest-sums.nim

@@ -0,0 +1,25 @@
+import std/heapqueue
+
+type cintArray = ptr UncheckedArray[cint]
+
+proc malloc(size: csize_t): pointer {.importc.}
+
+proc kSmallestPairs(a: cintArray, m: int, b: cintArray, n: int, k0: int, returnSize: ptr cint, returnColumnSizes: ptr cintArray): ptr UncheckedArray[cintArray] {.exportc.} =
+  let
+    k = min(k0, m*n)
+    sizes = cast[cintArray](malloc(cast[csize_t](cint.sizeof * k)))
+  var
+    h: HeapQueue[(cint, int32, int32)]
+  for i in 0..<min(m, k):
+    h.push (a[i]+b[0], cast[int32](i), 0'i32)
+  result = cast[ptr UncheckedArray[cintArray]](malloc(cast[csize_t](pointer.sizeof * k)))
+  returnSize[] = cast[cint](k)
+  returnColumnSizes[] = sizes
+  for i in 0..<k:
+    let (x, p, q) = h.pop
+    result[i] = cast[cintArray](malloc(cast[csize_t](cint.sizeof * 2)))
+    result[i][0] = a[p]
+    result[i][1] = b[q]
+    sizes[i] = 2
+    if q+1 < n:
+      h.push (a[p]+b[q+1], p, q+1)

find-k-th-smallest-pair-distance.nim

@@ -0,0 +1,22 @@
+# Find K-th Smallest Pair Distance
+import std/algorithm
+
+proc smallestDistancePair(nums: ptr UncheckedArray[cint], n: int, k: int): cint {.exportc.} =
+  var a = newSeq[cint](n)
+  for i in 0..<n: a[i] = nums[i]
+  a.sort()
+  var
+    l: cint = 0
+    h = a[^1]-a[0]
+  while l < h:
+    let m = (l+h) shr 1
+    var
+      i = 0
+      c = 0
+    for j in 0..<n:
+      while a[j]-a[i] > m:
+        inc i
+      c += cast[int](j-i)
+    if k <= c: h = m
+    else: l = m+1
+  l

kth-smallest-element-in-a-sorted-matrix.nim

@@ -0,0 +1,16 @@
+proc kthSmallest(matrix: ptr UncheckedArray[ptr UncheckedArray[cint]], n: int, ms: ptr UncheckedArray[cint], k: int): int {.exportc.} =
+  let m = ms[0]
+  var
+    l = matrix[0][0]
+    h = matrix[n-1][m-1]
+  while l < h:
+    let x = l+(h-l) div 2
+    var
+      c = 0
+      j = m
+    for i in 0..<n:
+      while j > 0 and x < matrix[i][j-1]: dec j
+      c += j
+    if c < k: l = x+1
+    else: h = x
+  l