Lower_bound functions and Upper_bound functions in C + +

The functions of binary lookup in STL are three Lower_bound, Upper_bound, Binary_search. These three functions are applied to the ordered interval (which is also the premise of using a binary search), and the two functions are recorded below.

Forwarditer Lower_bound (forwarditer First, Forwarditer last,const _tp& val) algorithm returns a non-descending sequence [first, last] The position of the first greater than or equal to Val in the value.

Forwarditer Upper_bound (forwarditer First, Forwarditer last, const _tp& val) The algorithm returns a non-descending sequence of the position in the "number" of the value Val.

Lower_bound and Upper_bound are as follows:

1.lower_bound function Source code:

View Sourceprint? 01. //这个算法中，first是最终要返回的位置 02. int  lower_bound( int  *array,  int  size,  int  key) 03. { 04. int  first =  0 , middle; 05. int  half, len; 06. len = size; 07.  08. while (len >  0 ) { 09. half = len >>  1 ; 10. middle = first + half; 11. if (array[middle] < key) {     12. first = middle +  1 ;          13. len = len-half- 1 ;        //在右边子序列中查找 14. } 15. else 16. len = half;             //在左边子序列（包含middle）中查找 17. } 18. return  first; 19. }

2.upper_bound function Source code:

View Sourceprint? 01. int  upper_bound( int  *array,  int  size,  int  key) 02. { 03. int  len = size- 1 ; 04. int  half, middle; 05.  06. while (len >  0 ){ 07. half = len >>  1 ; 08. middle = first + half; 09. if (array[middle] > key)      //中位数大于key,在包含last的左半边序列中查找。 10. len = half; 11. else { 12. first = middle +  1 ;     //中位数小于等于key,在右半边序列中查找。 13. len = len - half -  1 ; 14. } 15. } 16. return  first; 17. }

 

Lower_bound functions and Upper_bound functions in C + +