STL binary search: Hdu 5178 (bestcoder Round #31 1001)

The STL contains four different binary search algorithms ,binary_search lower_bound upper_bound equal_range. Their scopes are already sorted a good array.

★ Binary_search tries to find the element value in the sorted [first, last]. Returns true if it is found, or false if it does not return a lookup location.
★iterator lower_bound(const key_type &key): Returns an iterator that points to the key value >= key the first element. ★iterator upper_bound(const key_type &key): Returns an iterator that points to key values > Keys the first element. HDU 5178 Pairs

Problem Descriptionjohn has n Points on the X axis, and their coordinates is (x[I],0),(I=0,1,2,... ..,N?1) . He wants to know how many pairs <a,b> That |x[b]?x[a]|≤k.(a<b)
Inputthe first line contains a single integer T (about 5), indicating the number of cases.
Each test case begins with a integers N,k(1≤N≤100000,1≤k≤ ten 9 ) .
Next n Lines contain an integer x[I](? Ten 9 ≤x[I]≤ ten 9 ) , means the X coordinates.
Outputfor each case, output a integer means how many pairs <a,b> That |x[b]?x[a]|≤k .
Sample Input

25 5-10001001011025 300-1000100101102

Sample Output

310

Sourcebestcoder Round #31

Reference code one (using binary lookup function Upper_bound)

#include <iostream> #include <cstdio> #include <algorithm> #include <map> #include <vector > #include <queue> #include <cstring> #include <cmath> #include <climits> #define EPS 1e-10using namespace Std;typedef long long ll;const int inf=int_max;const int MAXN = 1e5+10;int N,k,a[maxn];int Main () {//  freopen ("Input.txt", "R", stdin);   int t;cin>>t;   while (t--) {    cin>>n>>k;    for (int i=0;i<n;i++) scanf ("%d", a+i);    Sort (a,a+n);    ll Ans=0;    for (int i=0;i<n;i++) {     ans+=upper_bound (a,a+n,a[i]+k)-a-1-i;//upper_bound return value-A gets the number of elements <=a[i]+k, Again-1 is to correct the initial position starting from 0, and the last minus I get is the pair number with I    }    printf ("%lld\n", ans);   }   return 0;}

Reference Code II (handwritten binary lookup function)

#include <iostream> #include <cstdio> #include <algorithm> #include <map> #include <vector > #include <queue> #include <cstring> #include <cmath> #include <climits> #define EPS 1e-10using namespace Std;typedef long long ll;const int inf=int_max;const int MAXN = 1e5+10;int N,k,a[maxn];ll Ans;int bin Ary_search (int num,int pos) {int low=pos+1,high=n-1,mid,res=0, while (Low<=high) {    mid= (low+high) >>1;    if (a[mid]-num>k) high=mid-1;    else{    res=mid-pos;//directly get the number of pair, or else to determine whether there is no result to deal with the    low=mid+1;}    }  Return res;//No then returns the initial value 0}int main () {  //Freopen ("Input.txt", "R", stdin);   int t;cin>>t;   while (t--) {    scanf ("%d%d", &n,&k);    for (int i=0;i<n;i++) scanf ("%d", a+i);    Sort (a,a+n);    ans=0;    for (int i=0;i<n;i++) {      ans+=binary_search (a[i],i);//cumulative Process    }    printf ("%lld\n", ans);   }   return 0;}

STL binary search: Hdu 5178 (bestcoder Round #31 1001)