ForwardIter lower_bound (ForwardIter first, ForwardIter last, const _Tp & val) algorithm returns a non-decreasing sequence [first, last) is not less than a first value val position.
ForwardIter upper_bound (ForwardIter first, ForwardIter last, const _Tp & val) algorithm returns a non-decreasing sequence [first, last) in the first position is greater than the value val.
lower_bound and upper_bound shown below: If all the elements is less than val, returns the last position and the last position is out of range! ! ~
2. Insert: for example as follows:
An array num sequence: To insert a number 3,9,20,111 4,10,11,30,69,70,96,100 provided. pos position to be inserted under the standard, then
lower_bound = POS ( NUM , NUM + 8,3) - NUM , POS = 0. I.e. num array subscript 0 position.
pos = lower_bound (num, num + 8,9) -num, pos = 1. I.e. num array index position 1 (i.e. located at position 10).
pos = lower_bound (num, num + 8,111) -num, pos = 8. I.e. num index array is at position 8 (subscript but the upper limit is 7, so the next element returns the last element).
pos = upper_bound (num, num + 8,20) -num, pos = 3. I.e. num array subscript 3 position.
1.lower_bound function source code:
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//这个算法中，first是最终要返回的位置
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int lower_bound(int *array, int size, int key)
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{
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int first = 0, middle;
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int half, len;
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len = size;
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while(len > 0) {
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half = len >> 1;
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middle = first + half;
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if(array[middle] < key) {
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first = middle + 1;
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len = len-half-1; //在右边子序列中查找
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}
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else
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len = half; //在左边子序列（包含middle）中查找
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}
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return first;
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}
2.upper_bound function source code:
01.
int upper_bound(int *array, int size, int key)
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{
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int len = size-1;
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int half, middle;
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while(len > 0){
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half = len >> 1;
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middle = first + half;
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if(array[middle] > key) //中位数大于key,在包含last的左半边序列中查找。
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len = half;
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else{
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first = middle + 1; //中位数小于等于key,在右半边序列中查找。
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len = len - half - 1;
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}
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}
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return first;
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}